Merged from trunk 5620:5629

Merged from trunk 5620:5629

Send the slot collision notice to stderr and only show minimal output in
--quiet mode.

Send the unmerge failure message to stderr.

Use end_paragraph(1) instead of add_line_break() so that there is really
a blank line.

For bug #144380, disable color at emerge startup and then enable it only
when it's absolutely sure that color should be enabled (after
EMERGE_DEFAULT_OPTS has been parsed).

Document PORTAGE_COMPRESS and PORTAGE_COMPRESS_FLAGS.

Obey the silent parameter when parsing options.

Fix a typo.

Catch InvalidData exceptions for bad atoms passed as emerge arguments.

svn path=/main/branches/prefix/; revision=5630