Consolidate "alias" directory to a method.

test/fast/Unit tests/nvm_alias_path

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+die () { echo $@ ; exit 1; }
+
+. ../../../nvm.sh
+
+[ "_$(nvm_alias_path)" = "_$NVM_DIR/alias" ] || die "nvm_alias_path did not requrn correct location"
+