[Felix-language] caching model

[john s. <sk...@us...>]

Here's another issue with caching: the binary caches depend on the flxg compiler build.

If you run

	flx --test=build/release blah

and then

	flx blah

all hell breaks loose. Similarly, you run rebuild the compiler and just run with --test=build/release
again, hell breaks loose again. Changing the install directory doesn't cause a problem
with the library includes because the flx files are in distinct places, but its the same application.

Some of the caches check the felix version, but that's not good enough.

Two options: change "binary" to the time stamp on flxg. Or just write a time stamp
into the cache, and wipe the whole thing if the compiler changes.

--
john skaller
sk...@us...