Adding feature check for babeltrace library [1], which will be used for
perf data file CTF [2] conversion in following patches.

The babeltrace library is now automatically detected as standard
feature. It's possible to specify LIBBABELTRACE_DIR make variable to
specify location of installed libbabeltrace, like:

  $ make LIBBABELTRACE_DIR=/opt/libbabeltrace/
    BUILD:   Doing 'make -j4' parallel build

  Auto-detecting system features:
  ...                         dwarf: [ on  ]
  ...                         glibc: [ on  ]
  ...                          gtk2: [ on  ]
  ...                      libaudit: [ on  ]
  ...                        libbfd: [ on  ]
  ...                        libelf: [ on  ]
  ...                       libnuma: [ on  ]
  ...                       libperl: [ on  ]
  ...                     libpython: [ on  ]
  ...                      libslang: [ on  ]
  ...                     libunwind: [ on  ]
  ...                 libbabeltrace: [ on  ]
  ...            libdw-dwarf-unwind: [ on  ]
  ...                          zlib: [ on  ]
  ...     DWARF post unwind library: libunwind

NOTE The installation of the [1] to to used by above make:
     $ git clone git://git.efficios.com/babeltrace.git
     $ cd babeltrace
     $ vim README
     $ ./bootstrap
     $ ./configure --prefix=/opt/libbabeltrace
     $ make prefix=/opt/libbabeltrace
     $ sudo make install prefix=/opt/libbabeltrace

Please make sure that the /opt/libbabeltrace/lib directory is in your
LD_LIBRARY_PATH:

 $ export LD_LIBRARY_PATH=/opt/libbabeltrace/lib

[1] babeltrace - http://www.efficios.com/babeltrace
[2] Common Trace Format - http://www.efficios.com/ctfSigned-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jeremie Galarneau <jgalar@efficios.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1424470628-5969-2-git-send-email-jolsa@kernel.orgSigned-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ Added missing babeltrace build instructions ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>