Don't mention "Unix" in native target name.

Don't mention "Unix" in native target name.

I find the mention of "Unix" unnecessary (and really slightly a lie)
on GNU/Linux in a couple of places:

 (gdb) maint print target-stack
 The current target stack is:
  - multi-thread (multi-threaded child process.)
  - child (Unix child process)
  - exec (Local exec file)
  - None (None)

 (gdb) help target child
 Unix child process (started by the "run" command).

 (gdb) target child
 Use the "run" command to start a Unix child process.

It's also odd that e.g., the Windows port says "Unix" in reaction to
"target child" (it was already that way before Windows used
inf-child.c):

 (gdb) target child
 Use the "run" command to start a Unix child process.
 (gdb)

So drop "Unix", going in the direction of saying mostly the same on
all native targets:

  (gdb) maint print target-stack
  The current target stack is:
   - multi-thread (multi-threaded child process.)
 - - child (Unix child process)
 + - child (Child process)
   - exec (Local exec file)
   - None (None)

  (gdb) help target child
 - Unix child process (started by the "run" command).
 + Child process (started by the "run" command).

 (gdb) target child
 -Use the "run" command to start a Unix child process.
 +Use the "run" command to start a child process.

gdb/
2014-03-13  Pedro Alves  <palves@redhat.com>

	* inf-child.c (inf_child_open, inf_child_target): Don't mention
	Unix in user visible strings.

gdb/testsuite/
2014-03-13  Pedro Alves  <palves@redhat.com>

	* gdb.base/default.exp: Update "target child" and "target procfs"
	tests to not expect "Unix".