[#4710] nanosecond precision in utime using libc futimens

[alexis779]

timeval & ufiles only provide microsecond precision. Use timespec & futimens from libc to implement File.ufile, to provide nanosecond precision.

This PR is required jnr/jnr-posix#107 to be able to use the native function.

Testing

test/utime.rb

F = '/tmp/test'
mtime = File.mtime(F)

File.utime(Time.now, mtime, F)
File.mtime(F) == mtime or raise "File.mtime should be == mtime"

JRuby error

$ touch /tmp/test
$ stat /tmp/test 
  File: /tmp/test
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 430953      Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/  alexis)   Gid: ( 1000/  alexis)
Access: 2017-09-23 15:50:57.974453385 -0700
Modify: 2017-09-23 15:50:57.974453385 -0700
Change: 2017-09-23 15:50:57.974453385 -0700
 Birth: -
$ ruby -v
jruby 9.1.12.0 (2.3.3) 2017-06-15 33c6439 OpenJDK 64-Bit Server VM 25.144-b01 on 1.8.0_144-8u144-b01-1-b01 +jit [linux-x86_64]
$ ruby test/utime.rb
RuntimeError: File.mtime should be == mtime
  <main> at test/utime.rb:6
$ stat /tmp/test 
  File: /tmp/test
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 430953      Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/  alexis)   Gid: ( 1000/  alexis)
Access: 2017-09-23 15:51:12.058870000 -0700
Modify: 2017-09-23 15:50:57.974453000 -0700
Change: 2017-09-23 15:51:12.062198429 -0700
 Birth: -

PR fix

$ bin/ruby -v
jruby 9.2.0.0-SNAPSHOT (2.4.1) 2017-09-23 0f9c2a3 OpenJDK 64-Bit Server VM 25.144-b01 on 1.8.0_144-8u144-b01-1-b01 +jit [linux-x86_64]
$ ruby test/utime.rb
$

[enebo]

@alexis779 I updated this to remove the conflicts but then realized your jnr-posix PR never got accepted. I asked about Windows support which will need to work or at least we will need to work around it not existing on that platform (although I did not check...they do have some of these methods on windows sometimes).

[headius]

Merged to master and 9.1.16.0.