add GOPATH support

Also fixes flex to depend on bison for its yacc implementation.

var/spack/repos/builtin/packages/flex/package.py

@@ -24,15 +24,18 @@
 ##############################################################################
 from spack import *
 
+
 class Flex(Package):
     """Flex is a tool for generating scanners."""
 
     homepage = "http://flex.sourceforge.net/"
-    url      = "http://download.sourceforge.net/flex/flex-2.5.39.tar.gz"
+    url = "http://download.sourceforge.net/flex/flex-2.5.39.tar.gz"
 
     version('2.6.0', '5724bcffed4ebe39e9b55a9be80859ec')
     version('2.5.39', 'e133e9ead8ec0a58d81166b461244fde')
 
+    depends_on("bison")
+
     def install(self, spec, prefix):
         configure("--prefix=%s" % prefix)