rdoc update.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@20917 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -6937,6 +6937,7 @@ VALUE pipe_close(VALUE args)
  *  If a block is given, the block is called and
  *  returns the value of the block.
  *  <i>read_io</i> and <i>write_io</i> are sent to the block as arguments.
+ *   In this form, read_io and write_io are closed when IO.pipe returns.
  *
  *  Not available on all platforms.
  *

thread.c

@@ -2006,7 +2006,7 @@ rb_thread_priority_set(VALUE thread, VALUE prio)
 #if defined(NFDBITS) && defined(HAVE_RB_FD_INIT)
 
 /*
- * several Unix platform supports file descriptors bigger than FD_SETSIZE
+ * several Unix platforms supports file descriptors bigger than FD_SETSIZE
  * in select(2) system call.
  *
  * - Linux 2.2.12 (?)