perf: don't clobber startrev variable
Previously, the "startrev" argument would be ignored due to
"startrev = 0" in the benchmark function. This meant that
`hg perfrevlog` always started at revision 0.
Rename the local variable to "beginrev" so the variable does the
right thing.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing:
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
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