copies: add a config to limit the number of candidates to check in heuristics
The heuristics algorithm find possible candidates for move/copy and then check
whether they are actually a copy or move. In some cases, there can be lot of
candidates possible which can actually slow down the algorithm.
This patch introduces a config option
`experimental.copytrace.movecandidateslimit` using which one can limit the
candidates to check. The limit defaults to 100.
Thanks to Yuya for suggesting to skip copytracing for that file with a
warning.
Differential Revision: https://phab.mercurial-scm.org/D987
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL