FIXED: crash when a second Epilog window is deleted

Updates xpce.  The terminals share the interned Colour objects of their
palette but held them with a flag rather than a count, so deleting one
Epilog window freed colours the others were still painting with.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T13zyETRgTwZhjk383aj5n

Author: JanWielemaker