Make the maint.exp:'maint print objfiles' test less fragile.

Make the maint.exp:'maint print objfiles' test less fragile.

I was "lucky" enough that an unrelated patch changed how many symtabs
GDB expands in a plain run to main, and that triggered a latent issue
in this test:

  PASS: gdb.base/maint.exp: maint print objfiles: header
  PASS: gdb.base/maint.exp: maint print objfiles: psymtabs
  FAIL: gdb.base/maint.exp: maint print objfiles: symtabs

The problem is in my case, expect is managing to alway put in the
buffer chunks like this:

  Psymtabs:
  ../../../src/gdb/testsuite/gdb.base/break1.c at 0x1ed2280, ../../../src/gdb/testsuite/gdb.base/break.c at 0x1ed21d0,

  Symtabs:
  ../../../src/gdb/testsuite/gdb.base/break.c at 0x1f044f0, /usr/include/stdio.h at 0x1ed25a0, /usr/include/libio.h at 0x1ed2510, /usr/include/bits/types.h at 0x1ed2480, /usr/lib/gcc/x86_64-redhat-linux/4.7.2/include/stddef.h at 0x1ed23f0,

  Object file /usr/lib/debug/lib64/ld-2.15.so.debug:  Objfile at 0x1f4bff0, bfd at 0x1f2d940, 0 minsyms

  Psymtabs:
  bsearch.c at 0x1f65340, ../sysdeps/x86_64/multiarch/init-arch.c at
  0x1f65290, ...

Note: Psymtabs:/Symtabs:/Psymtabs:.

So, the loop matches the first Psymtabs in the buffer.  Then we're
left with

  ../../../src/gdb/testsuite/gdb.base/break1.c at 0x1ed2280, ../../../src/gdb/testsuite/gdb.base/break.c at 0x1ed21d0,

  Symtabs:
  ../../../src/gdb/testsuite/gdb.base/break.c at 0x1f044f0, /usr/include/stdio.h at 0x1ed25a0, /usr/include/libio.h at 0x1ed2510, /usr/include/bits/types.h at 0x1ed2480, /usr/lib/gcc/x86_64-redhat-linux/4.7.2/include/stddef.h at 0x1ed23f0,

  Object file /usr/lib/debug/lib64/ld-2.15.so.debug:  Objfile at 0x1f4bff0, bfd at 0x1f2d940, 0 minsyms

  Psymtabs:
  bsearch.c at 0x1f65340, ../sysdeps/x86_64/multiarch/init-arch.c at
  0x1f65290, ...

In the next iteration, because the psymtabs regex comes first, we
match with the Psymtabs: line, then of course, end up with just

  bsearch.c at 0x1f65340, ../sysdeps/x86_64/multiarch/init-arch.c at
  0x1f65290, ...

in the buffer.  The "Symtabs:" line is lost.  expect then reads more
gdb output, and manages to again retrieve the same pattern.  Rinse,
repeat, and the test never matches any "Symtab:" line.

We don't know the order the matches lines will appear, so the fix is
to consume one line at a time, and run it through all three milestone
regexes.

gdb/testsuite/
2013-11-20  Pedro Alves  <palves@redhat.com>

	* gdb.base/maint.exp (maint print objfiles): Consume one line at a
	time, and run it through all three milestone regexes.