Implement "-n <n>" flag for repeated posix_fadvise()
Add explanation of -n flag / NOCACHE_NR_FADVISE env variable
nocache retrieves max fds from actual process limits.
Merge remote-tracking branch 'noushi/behavior_mods'

* noushi/behavior_mods:
  nocache retrieves max fds from actual process limits.
Only do multi-fadvise if previous call was successful

Reported-by: Reda Noushi <reda@logzilla.pro>

> one remark: what should nocache do if a non-zero value is returned by posix_fadvise()?
> 1. is it okay to continue executing it and returning the last value?
> 2. or stop execution and return the last non-zero value of fadv()?
Update man pages to reflect "-n" option
Merge branch 'n-times-fadvise'

* n-times-fadvise:
  Update man pages to reflect "-n" option
  Only do multi-fadvise if previous call was successful
  Add explanation of -n flag / NOCACHE_NR_FADVISE env variable
  Implement "-n <n>" flag for repeated posix_fadvise()

There was a trivial-to-solve merge conflict in nocache.c
Correct testlib output

(Otherwise `prove` would complain about “out of sequence” tests.)