Add `nvm_is_iojs_version`

nvm.sh

@@ -354,6 +354,10 @@ nvm_node_prefix() {
   echo "node"
 }
 
+nvm_is_iojs_version() {
+  [ "_$(echo "$1" | cut -c1-5)" = "_iojs-" ]
+}
+
 nvm_ls() {
   local PATTERN
   PATTERN="$1"
@@ -1198,6 +1202,7 @@ nvm() {
     "unload" )
       unset -f nvm nvm_print_versions nvm_checksum \
         nvm_iojs_prefix nvm_node_prefix \
+        nvm_is_iojs_version \
         nvm_ls_remote nvm_ls nvm_remote_version \
         nvm_version nvm_rc_version \
         nvm_version_greater nvm_version_greater_than_or_equal_to \

test/fast/Unit tests/nvm_is_iojs_version

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+die () { echo $@ ; exit 1; }
+
+. ../../../nvm.sh
+
+nvm_is_iojs_version 'iojs-' || die '"nvm_is_iojs_version iojs- was not true'
+nvm_is_iojs_version 'iojs-foo' || die '"nvm_is_iojs_version iojs- was not true'
+! nvm_is_iojs_version 'iojs' || die '"nvm_is_iojs_version iojs was not false'
+! nvm_is_iojs_version 'v1.0.0' || die '"nvm_is_iojs_version v1.0.0" was not false'