ext/File-Glob/t/rt131211.t: fix timing issues

ext/File-Glob/t/rt131211.t: fix timing issues

This test file occasionally fails test numbers 1 and/or 2 on smokes.
These two tests measure how long it takes to do a matching and
non-matching glob() with a lot of "a*a*a*...." and fail if the
match and non-matching times differ too much (the original bug was that
non-match went exponential on number of "a*"'s).

However, on good systems, the timings returned are typically
sub-millisecond, so I'm guessing the occasional failures are due to

(small measured noise) * 100  > (another small measured noise).

So this commit avoids tests 1&2 failing unless the values measured
are large enough not to be merely noise.

This is just speculation on my part though - I couldn't reproduce a
failure myself.