t/perf/fsmonitor: perf comparison of multiple fsmonitor integrations

t/perf/fsmonitor: perf comparison of multiple fsmonitor integrations

Allows for simple perf comparison of different integrations. I ran it
to compare our perl script w/ rs-git-fsmonitor and found 20-30ms of
overhead on every command.

Output looks like this (extra newlines added for readability)

Test                                                        this tree
---------------------------------------------------------------------------
7519.4: status (fsmonitor=query-watchman)                   0.42(0.37+0.05)
7519.5: status -uno (fsmonitor=query-watchman)              0.19(0.12+0.07)
7519.6: status -uall (fsmonitor=query-watchman)             1.36(0.73+0.62)
7519.7: diff (fsmonitor=query-watchman)                     0.14(0.09+0.05)
7519.8: diff -- 0_files (fsmonitor=query-watchman)          0.14(0.11+0.03)
7519.9: diff -- 10_files (fsmonitor=query-watchman)         0.14(0.10+0.04)
7519.10: diff -- 100_files (fsmonitor=query-watchman)       0.14(0.09+0.05)
7519.11: diff -- 1000_files (fsmonitor=query-watchman)      0.14(0.08+0.06)
7519.12: diff -- 10000_files (fsmonitor=query-watchman)     0.14(0.09+0.05)
7519.13: add (fsmonitor=query-watchman)                     2.04(1.32+0.66)

7519.16: status (fsmonitor=rs-git-fsmonitor)                0.39(0.32+0.08)
7519.17: status -uno (fsmonitor=rs-git-fsmonitor)           0.17(0.11+0.06)
7519.18: status -uall (fsmonitor=rs-git-fsmonitor)          1.33(0.71+0.61)
7519.19: diff (fsmonitor=rs-git-fsmonitor)                  0.11(0.07+0.04)
7519.20: diff -- 0_files (fsmonitor=rs-git-fsmonitor)       0.11(0.09+0.03)
7519.21: diff -- 10_files (fsmonitor=rs-git-fsmonitor)      0.11(0.09+0.03)
7519.22: diff -- 100_files (fsmonitor=rs-git-fsmonitor)     0.11(0.07+0.04)
7519.23: diff -- 1000_files (fsmonitor=rs-git-fsmonitor)    0.11(0.06+0.06)
7519.24: diff -- 10000_files (fsmonitor=rs-git-fsmonitor)   0.11(0.06+0.06)
7519.25: add (fsmonitor=rs-git-fsmonitor)                   2.03(1.28+0.69)

7519.28: status (fsmonitor=disabled)                        0.77(0.59+0.99)
7519.29: status -uno (fsmonitor=disabled)                   0.42(0.33+0.85)
7519.30: status -uall (fsmonitor=disabled)                  1.59(1.02+1.34)
7519.31: diff (fsmonitor=disabled)                          0.35(0.30+0.81)
7519.32: diff -- 0_files (fsmonitor=disabled)               0.11(0.08+0.04)
7519.33: diff -- 10_files (fsmonitor=disabled)              0.11(0.07+0.04)
7519.34: diff -- 100_files (fsmonitor=disabled)             0.11(0.08+0.03)
7519.35: diff -- 1000_files (fsmonitor=disabled)            0.11(0.10+0.02)
7519.36: diff -- 10000_files (fsmonitor=disabled)           0.12(0.07+0.06)
7519.37: add (fsmonitor=disabled)                           2.24(1.48+1.44)

Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>