use lstat(2) to check if it's a symlink
tests for File.socket? and File.symlink?
add `cmd` (command output expression).
STDERR's file descriptor is 2.

closes #1
use array parameter on IO.open.
Catch up with API changes on mrb_intern() -> mrb_intern_cstr()
Merge pull request #2 from pbosetti/master

Catch up with API changes on mrb_intern() -> mrb_intern_cstr()
suppress a warning and fix a possible segv.
remove duplicated white spaces.
add File#flock.
fix descriptor leakage.
don't retry when we cannot fork(2).

EAGAIN indicates the system is under heavy load.
Retrying make things worse.
style
syswrite must write to fd2 if it is properly set.

closes #3.
Truncate file on File.open(file, "w")
Merge branch 'master' of https://github.com/iij/mruby-io
Merge pull request #4 from pbosetti/master

Truncate the file to zero length on opening when "w" mode is set
fix RSTRING_PTR usage.
fix typo...
IO.sysopen raises an exception when open(2) fails.  closes #6.