Support --install option upon sourcing.

test/sourcing/Sourcing nvm.sh with --install and .nvmrc should install it

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+die () { echo $@ ; exit 1; }
+
+echo '0.10.2' > ../../.nvmrc || die 'creation of .nvmrc failed'
+
+. ../../nvm.sh --install
+EXIT_CODE="$(echo $?)"
+
+echo 'sourcing complete.'
+
+nvm_version 0.10.2 >/dev/null 2>&1 || die "v0.10.2 not installed: $(nvm ls)"
+
+[ "_$(nvm_rc_version | \grep -o -e 'with version .*$')" = "_with version <0.10.2>" ] || die "nvm_rc_version $(nvm_rc_version)"
+
+[ "_$EXIT_CODE" = "_0" ] || die "sourcing returned nonzero exit code: $EXIT_CODE"
+
+NVM_LS_CURRENT="$(nvm ls current | \grep -o v0.10.2)"
+[ "_$NVM_LS_CURRENT" = '_v0.10.2' ] || die "'nvm ls current' did not return '-> v0.10.2', got '$NVM_LS_CURRENT' `nvm ls`"
+