[OpenSCAD] Caching files?

[Marius Kintel]

Hi again,

This problem happens because there is no dependency tracking on libraries (aka. USE'd modules).
Libraries are precompiled and the compiled library (called a Module) is cached with the filename and timestamp as a key in the cache dictionary. Since dependency tracking isn't implemented, the cache doesn't see the underlying changes.

Some notes:
o There was a bug in Flush Caches - it didn't flush the library cache. This is now fixed in the master branch.
o I'm not sure how much value there is in caching compiled libraries. Maybe it's an unnecessary optimization.
o Dependency tracking is just a global list of files. This could be changed into being a per-module dependency tracker.

 -Marius