ports-mgmt/portmaster: fix 2 issues in --clean-distfiles

There was no need to deal with distfile names that contained embedded
blanks or characters with special meaning in file glob patterns, but
this has changed with file names derived from repository URIs or other
naming systems.

This update fixes 2 issues reported by Daniel Rossberg on GitHub:

• issue #75: --clean-distfiles cannot handle paths with spaces
• issue #76: --clean-distfiles with paths containing square brackets

Reported by: Daniel Rossberg