#62 Adding parallel compiling support (another)

[David Falkinder]

Related to feature request 2037601, and existing patch 2791045

This is a slightly different approach to the existing patch, and almost certainly a lot less polished. It's more ideas rather than an alternative.

It makes use of the 'ExecutorService' provided in Java 1.5+ to thread out the CommandLineCompiler jobs.

Consider this a proof of concept - i.e. it needs taking forward by someone with Java skills ( i.e. not me )

Notes :

- At the moment, the thread count == host cpu count. This should probably be made configurable.
- It's only been tested with gcc, but performs well, drastically reducing large project build times
- Bad things happen if you use PCH with threaded compilers ( effectively they all fight to write the pch ).
- Requires the javac.target and source to be changed from 1.1 to 1.5

I hope this helps someone deliver parallel compilation to cpptasks, as it's a real value add.

[David Falkinder]