Improve minifiers to capture error from UglifyJS.
Improve minifiers to capture error from UglifyJS.

The error messages which come from UglifyJS tend to be quite cryptic, as
seen in issues like meteor/meteor#8370 or meteor/meteor#8020.  The file,
line, and column are provided, however the message is garbled and the
stacktrace long and acutely harrowing.  Since these errors are occurring
on automatically concatenated files, even the line number is sometimes
not helpful.  Additionally, sourceMaps are not available in production
builds, intentionally.  (I wasn't able to access them from
`file.getSourceMap()` or `file.sourceMap` at all.)

In addition to actually providing the name of the encapsulating file,
which provides _some_visibility, this commit implements a parser around
the UglifyJS error which detects the error and location information of
the error, seeks to the line in the concatenated source, reads the
inline filename, and provides it in the output.

Crude, but incredibly helpful in diagnosing this problem until a better
solution is reached.

Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor