Conditional Z1 breakpoint hangs GDBserver.

While trying to fix hbreak2.exp against GDBserver I noticed this...

 (gdb) hbreak main if 1
 Sending packet: $m400580,40#2e...Packet received: e8d2ffffff5dc3554889e54883ec10c745fc00000000eb0eb800000000e8c1ffffff8345fc01817dfce70300007ee9b800000000c9c3662e0f1f840000000000
 Sending packet: $m40058f,1#31...Packet received: c7
 Hardware assisted breakpoint 1 at 0x40058f: file ../../../src/gdb/testsuite/gdb.base/break-idempotent.c, line 46.
 Sending packet: $Z1,40058f,1;X3,220127#9b...
 *hangs forever*

The issue is that nothing advances the packet pointer if
add_breakpoint_condition either fails to parse the agent expression,
or fails to find the breakpoint, resulting in an infinite loop in
process_point_options.  The latter case should really be fixed by
GDBserver tracking GDB Z1 breakpoints in its breakpoint structures
like Z0 breakpoints are, but the latter case still needs handling.
add_breakpoint_commands has the same issue, though at present I don't
know any way to trigger it other than sending a manually cooked
packet.

Unbelievably, it doesn't look like we have any test that tries setting
a conditional hardware breakpoint.  Looking at cond-eval-mode.exp, it
looks like the file was meant to actually test something, but it's
mostly empty today.  This patch adds tests that tries all sorts of
conditional breakpoints and watchpoints.  The test hangs/fails without
the GDBserver fix.

Tested on x86_64 Fedora 17.

gdb/gdbserver/
2014-04-10  Pedro Alves  <palves@redhat.com>

	* mem-break.c (add_breakpoint_condition, add_breakpoint_commands):
	Check if the condition or command is NULL before checking if the
	breakpoint is known.  On success, return true.
	* mem-break.h (add_breakpoint_condition): Document return.
	(add_breakpoint_commands): Add describing comment.
	* server.c (skip_to_semicolon): New function.
	(process_point_options): Use it.

gdb/testsuite/
2014-04-10  Pedro Alves  <palves@redhat.com>

	* gdb.base/cond-eval-mode.c: New file.
	* gdb.base/cond-eval-mode.exp: Use standard_testfile.  Adjust
	prepare_for_testing to build the new file.  Check result of
	runto_main.
	(test_break, test_watch): New procedures.
	(top level): Use them.