Source files are copied to the out directory

[gebner]

1. make copies the source files to out
2. Go-to-definition in the test/ directory leads to out
3. I accidentally modify files in out
4. make silently reverts my changes on the next build

This has bitten me so many times now. I'm really tired of the out business. We need to fix this.

• Could we symlink instead of copy?
• Or at least make the files read-only?
• Or do away with out entirely?

A related issue is that we have two copies of pulse.cmxs, and make plugin only updates one of them.