This version fixes a critical bug [1] that prevents us from simplifying
bucklets intergration. In this version, Buck only allows defining new
rule functions in files included with include_defs, not actually
instantiating rules, so we need to reshuffle some rules.
After this commit [2] "$(macro ...)" syntax is preserved for buck
macros, we need to use a backslash to send commands directly to the
shell: "\$(macro ...)". It turns out this doesn't work yet, shell
backticks seem to work though [3].
[1] https://github.com/facebook/buck/issues/182
[2] d6f3252170
[3] https://github.com/facebook/buck/issues/212
Change-Id: Ie99757bafc626d4ac2c5a75a2983d91b0c4f6d24
7fc13dca82