compilation-mode: improve parsing of error messages.

[mookid]

• parse location such as previous declaration at .\client.go:131:47

correctly, and make them information-level error (errors are underlined by default in green and are skipped by next-error by default).

I did not find other error messages referencing locations in the compiler code, but I'll be glad to handle more if necessary.

• do not underline error message space following the last colon of the notation:

this underlining:

.\info.go:64:6: informative message
^^^^^^^^^^^^^^

rather than this one:

.\info.go:64:6: informative message
^^^^^^^^^^^^^^^^