Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/extsprintf/Makefile

@@ -0,0 +1,24 @@
+#
+# Copyright (c) 2012, Joyent, Inc. All rights reserved.
+#
+# Makefile: top-level Makefile
+#
+# This Makefile contains only repo-specific logic and uses included makefiles
+# to supply common targets (javascriptlint, jsstyle, restdown, etc.), which are
+# used by other repos as well.
+#
+
+#
+# Files
+#
+JSL		 = jsl
+JSSTYLE		 = jsstyle
+JS_FILES	:= $(shell find examples lib -name '*.js')
+JSL_FILES_NODE   = $(JS_FILES)
+JSSTYLE_FILES	 = $(JS_FILES)
+JSL_CONF_NODE	 = jsl.node.conf
+
+# Default target is "check"
+check:
+
+include ./Makefile.targ