blackbox: fix rotation with chg The added test will show: $ $PYTHON showsize.py .hg/blackbox* .hg/blackbox.log: < 500 .hg/blackbox.log.1: < 500 .hg/blackbox.log.2: < 500 .hg/blackbox.log.3: < 500 .hg/blackbox.log.4: < 500 .hg/blackbox.log.5: >= 500 with previous code. The issue is caused by blackbox caching file objects *by path*, and the rotation size check could run on a wrong file object (i.e. it should check "blackbox.log", but `filehandles["blackbox.log"]` contains a file object that has been renamed to "blackbox.log.5"). This patch removes the "filehandlers" global cache added by 45313f5a3a8c to solve the issue. I think the original patch was trying to make different ui objects use a same file object if their blackbox.log path is the same. In theory it could also be problematic in the rotation case. Anyway, that should become unnecessary after D650. Differential Revision: https://phab.mercurial-scm.org/D648