Added sourceRefOverrides for commit ref overrides of github sources.

Added mapAttrValues for mapping over an attrset to update the value.

Actual implementation of makeSafeName.

Add makeSafeName function.

Remove debug tracing from -src input handling.

Optional cleaning of -src input depending on type.

Add tracing for type of -src input argument for hydra debugging.

Remove debugging trace output from source cleaning.

Apply clean filters to input -src overrides.

Filter .ghc.environment files from sources as well as cabal output dirs.

Clean sources of build/dev output when specified via local.

Disable addition of cabal-install tool to packages when in nix shell.

Fix spelling error in comment.

Allow missing subpath sources (for new modules in a submodule repo).

Add checkAttrValuePathExists to devnix to allow non-aborting test.