Add --funcs to show available functions in symtab.

Originally this feature came from Srikar's uprobes patches
( http://lkml.org/lkml/2010/8/27/244 )

e.g.
...
__ablkcipher_walk_complete
__absent_pages_in_range
__account_scheduler_latency
__add_pages
__alloc_pages_nodemask
__alloc_percpu
__alloc_reserved_percpu
__alloc_skb
__alloc_workqueue_key
__any_online_cpu
__ata_ehi_push_desc
...

This also supports symbols in module, e.g.

...
cleanup_module
cpuid_maxphyaddr
emulate_clts
emulate_instruction
emulate_int_real
emulate_invlpg
emulator_get_dr
emulator_set_dr
emulator_task_switch
emulator_write_emulated
emulator_write_phys
fx_init
...

Original-patch-from: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: 2nddept-manager@sdl.hitachi.co.jp
Cc: Franck Bui-Huu <fbuihuu@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20110113124611.22426.10835.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
[ committer note: Add missing elf.h for STB_GLOBAL that broke a RHEL4 build ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>