Two enhancements to PEXBuilder:
Review Request #2346 — Created June 11, 2015 and submitted
1. Allow it to optionally copy instead of hard-linking files into the environment. This is useful for creating long-running environments without corrupting them by modifying the underlying files from under them. 2. Make precompiling .py sources optional, as mentioned in a TODO. Again, in long-running environments it may make more sense to save this time when building the environment and pay it when actually using the environment.
Added tests for the new functionality.
CI passes: https://travis-ci.org/pantsbuild/pex/builds/66359462