Update Makefile to pass the -L flag for lua
Don't add -L for /usr/local/lib

This really should detect the prefix for rustc and avoid adding the -L
for that prefix, but for my purposes, filtering out /usr/local/lib is
sufficient.

This still doesn't compile right on OS X Yosemite, but it should work on
other OS's for now.
Update to latest rustc (0.12.0-pre eaf810a21)