[Fix] nvm_hash_reset: only run hash -r where the shell supports it

Under bash's `set +h`, `hash -r` errors with "hash: hashing disabled",
which is then printed on every `nvm use`, including the one at shell startup.

Guarding on `$-` alone would be wrong:
`zsh` never puts `h` in `$-` - there `h` is `HIST_IGNORE_DUPS` -
and `dash` has no `h` flag at all,
so it would skip the call in 3 of the 4 shells the fast suite runs.

Gate on the shell instead, and skip only where the call fails:
bash under `set +h`, and `ksh93`, whose `hash` takes no `-r` and whose
usage error aborts `nvm use` before it can export `NVM_BIN`.
`ksh` is detected by probing rather than by version,
so `mksh` and `pdksh`, which do accept `-r`, keep getting the call.

The `${-#*h}` test is from #3910.

Refs #2065
Refs #3247

test/fast/Running 'nvm use' and 'nvm deactivate' with hashing disabled

@@ -0,0 +1,45 @@
+#!/bin/bash
+
+# the `bash` shebang is deliberate: only bash can exhibit the bug, so pinning
+# it keeps this meaningful in every job of the shell matrix
+
+die () { echo "$@" ; cleanup ; exit 1; }
+cleanup () {
+  set -h
+  rm -f "${OUTPUT_FILE-}"
+}
+
+export NVM_DIR="$(cd ../.. && pwd)"
+
+: nvm.sh
+\. ../../nvm.sh
+\. ../common.sh
+
+make_fake_node v0.2.3 || die 'unable to make fake node'
+
+OUTPUT_FILE="$(mktemp)"
+
+set +h
+
+# not in a command substitution, so the `PATH` it sets survives to `nvm deactivate`
+nvm use --delete-prefix v0.2.3 > "${OUTPUT_FILE}" 2>&1
+OUTPUT="$(cat "${OUTPUT_FILE}")"
+case "${OUTPUT}" in
+  *'hash: '*) die "nvm use complained about hashing: ${OUTPUT}" ;;
+esac
+case "${OUTPUT}" in
+  *'Now using node v0.2.3'*) ;;
+  *) die "nvm use did not activate v0.2.3: ${OUTPUT}" ;;
+esac
+
+nvm deactivate > "${OUTPUT_FILE}" 2>&1
+OUTPUT="$(cat "${OUTPUT_FILE}")"
+case "${OUTPUT}" in
+  *'hash: '*) die "nvm deactivate complained about hashing: ${OUTPUT}" ;;
+esac
+case "${OUTPUT}" in
+  *'removed from ${PATH}'*) ;;
+  *) die "nvm deactivate did not strip the nvm bin dir: ${OUTPUT}" ;;
+esac
+
+cleanup

test/fast/Running 'nvm use' does not leave a stale hashed node

@@ -0,0 +1,29 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../.. && pwd)"
+
+: nvm.sh
+\. ../../nvm.sh
+\. ../common.sh
+
+make_fake_node v0.2.3 || die 'unable to make fake node v0.2.3'
+make_fake_node v0.10.1 || die 'unable to make fake node v0.10.1'
+
+nvm use --delete-prefix v0.2.3 >/dev/null 2>&1 || die 'failed to activate v0.2.3'
+
+# run `node` from this shell, so that the shell caches where it found it
+node >/dev/null 2>&1 || die 'fake node v0.2.3 is not runnable'
+
+nvm use --delete-prefix v0.10.1 >/dev/null 2>&1 || die 'failed to activate v0.10.1'
+
+ACTUAL="$(node)"
+[ "${ACTUAL}" = 'v0.10.1' ] || die "expected node v0.10.1 after switching versions, got '${ACTUAL}'"
+
+nvm deactivate >/dev/null 2>&1 || die 'failed to deactivate'
+
+RESOLVED="$(command -v node || true)"
+case "${RESOLVED}" in
+  "${NVM_DIR}"/*) die "after deactivating, node still resolves inside \${NVM_DIR}: ${RESOLVED}" ;;
+esac

test/fast/Unit tests/nvm_hash_reset

@@ -0,0 +1,27 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+: nvm.sh
+\. ../../../nvm.sh
+
+# also covers #3247, where `command hash -r` found a `hash` binary, not the builtin
+OUTPUT="$(nvm_hash_reset 2>&1)"
+RC=$?
+[ ${RC} -eq 0 ] || die "nvm_hash_reset returned ${RC}: ${OUTPUT}"
+[ -z "${OUTPUT}" ] || die "nvm_hash_reset was not silent: ${OUTPUT}"
+
+# bash is the only supported shell that can turn hashing off
+if [ -n "${BASH_VERSION-}" ]; then
+  set +h
+  OUTPUT="$(nvm_hash_reset 2>&1)"
+  RC=$?
+  set -h
+  [ ${RC} -eq 0 ] || die "with hashing disabled, nvm_hash_reset returned ${RC}: ${OUTPUT}"
+  [ -z "${OUTPUT}" ] || die "with hashing disabled, nvm_hash_reset was not silent: ${OUTPUT}"
+
+  ls >/dev/null 2>&1
+  hash -t ls >/dev/null 2>&1 || die 'expected `ls` to be hashed'
+  nvm_hash_reset || die 'with hashing enabled, nvm_hash_reset failed'
+  ! hash -t ls >/dev/null 2>&1 || die 'nvm_hash_reset did not clear the hash table'
+fi