Make Mix.SystemVersionError message more meaningful
Merge pull request #1450 from meh/mix-elixir

Make Mix.SystemVersionError message more meaningful
Upated test cases to support compilation halting on first failed compiler. Updated existing tests to handle CompileError being thrown on failure.

Updated compile tasks to raise exceptions after compiling all files
Updated tests to verify exceptions raised
Always load paths on app.start, even with --no-compile
Move the Elixir version requirement check to a better place
Merge pull request #1452 from meh/mix-version

Move the Elixir version requirement check to a better place
Document mix loadpaths and app.start options
Merge pull request #1449 from jwarwick/issue_1441

Possible fix for Issue #1441
Slight clean up on mix tests

We don't need to test all scenarios because guaranteeing that
a failure in one compiler is enough to abort the others is enough
for an integration test.