Merge pull request #4 from delcypher/master

Various Improvements
Fixed import errors for "as" caused by trying to import
driver.popenwrapper
Enabled popenwrapper and logging in driver/as
The LLVM_COMPILER_PATH environment variable is now used for running
llvm-as
Added some helpful logging to "as"
Emit warning in attachBitcodePathToObject() if we encounter a non-object
file instead of being silent.
Added helpful comment about how driver/as is invoked.
Merge pull request #6 from delcypher/fixes

Mostly fixes for "as"