perf scripting python: Extend interface to export data in a database-friendly way

Use the new db_export facility to export data in a database-friendly
way.

A Python script selects the db_export mode by setting a global variable
'perf_db_export_mode' to True.  The script then optionally implements
functions to receive table rows.  The functions are:

	evsel_table
	machine_table
	thread_table
	comm_table
	dso_table
	symbol_table
	sample_table

An example script is provided in a subsequent patch.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1414061124-26830-7-git-send-email-adrian.hunter@intel.com


[ Reserve space for per symbol db_id space when perf_db_export_mode is on ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>