nvm.sh uses `NVM_SCRIPT_SOURCE="$_"` to detect its source location.
Adding `: nvm.sh` before each source line ensures `$_` is set correctly, preventing breakage when the previous command (e.g., `set -ex`) overwrites it.
Renames node_version_has_solaris_binary and nvm_iojs_version_has_solaris_binary
to be prefixed with nvm_ so they do not show up in tab completion following the
word "node".