Add filters support for available variable list.

Default filter is "!__k???tab_*&!__crc_*" for filtering out
automatically generated symbols.

The format of filter rule is "[!]GLOBPATTERN", so you can use wild
cards. If the filter rule starts with '!', matched variables are filter
out.

e.g.:
 # perf probe -V schedule --externs --filter=cpu*
Available variables at schedule
        @<schedule+0>
                cpumask_var_t   cpu_callout_mask
                cpumask_var_t   cpu_core_map
                cpumask_var_t   cpu_isolated_map
                cpumask_var_t   cpu_sibling_map
                int     cpu_number
                long unsigned int*      cpu_bit_bitmap
		...

Cc: 2nddept-manager@sdl.hitachi.co.jp
Cc: Chase Douglas <chase.douglas@canonical.com>
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: <20110120141539.25915.43401.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
[ committer note: Removed the elf.h include as it was fixed up in e80711ca]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>