Minor rebar and eunit integration improvements

[mbystryantsev]

Offer some rebar integration improvements:

• Boost debug session start time by selective modules interpreting.
• Check conent roots for rebar.config.script too.
• Valid Windows-specific file URLs handling (like file://C:/../../)
• Allow to specify custom config.rebar / config.rebar.script.
• Allow to use ebin / .eunit directories as module paths when running eunit configuration.
• Do not check for dirty files when rebar used, delegate it to rebar.
• Clean module before compile if forced build flag set.