This means File.chmod, File.lchmod, File.chown, File.lchown,
File.unlink, and File.utime operations on slow filesystems
no longer hold up other threads.

The platform-specific utime_failed changes is compile-tested
using a new UTIME_EINVAL macro

This hurts performance on fast filesystem, but these methods
are unlikely to be performance bottlenecks and (IMHO) avoiding
pathological slowdowns and stalls are more important.

benchmark results:
minimum results in each 3 measurements.
Execution time (sec)
name	trunk	built
file_chmod	0.591	0.801

Speedup ratio: compare with the result of `trunk' (greater is better)
name	built
file_chmod	0.737

* file.c (UTIME_EINVAL): new macro to ease compile-testing
* file.c (struct apply_arg): new struct
* file.c (no_gvl_apply2files): new function
* file.c (apply2files): release GVL
* file.c (chmod_internal): adjust for apply2files changes
* file.c (lchmod_internal): ditto
* file.c (chown_internal): ditto
* file.c (lchown_internal): ditto
* file.c (utime_failed): ditto
* file.c (utime_internal): ditto
* file.c (unlink_internal): ditto
  [ruby-core:83200] [Feature #13996]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60386 b2dd03c8-39d4-4d8f-98ff-823fe69b080e