Merge pull request #137 from ret2libc/master

userspace/libsinsp/filter: fix a wrong merge about quotes in filters
move the fileslower chisel into the performance group
added the ability to specify custom chisel directories using the SYSDIG_CHISEL_DIR environment variable
the table_generator can now concatenate multiple keys
the topconns chisel now shows the L4 protocol
sendto and recvfrom modify the state, so the filtering system should let them go through the parser
Fix warning on 32 bit
Kernel coding style: comments
Kernel coding style: whitespaces
compilation errors
Ignore duplicated chisels

This will make sysdig ignore chisels with the same name as one
already added to the list.

This currently follows the follow priority on path: . -> ~/.chisels ->
/usr/share/sysdig/chisels (this last one depends on
MAKE_INSTALL_PREFIX).
The order is the same set for paths when libsinsp is initialized.
Refactoring of sinsp_chisel::get_chisel_list
More refactoring of sinsp_chisel::get_chisel_list
fix warning on OSX
thread.totexectime filter field
compile error
Experiment to compile sysdig on GCC 4.5 (EL6) as well
Explicit CXX
Make sysdig compile again on GCC 4.5 (less readable code, but a bunch of people still use EL6)
Implements #22 JSON output

Introduces a JSON root in every tostring call of
sinsp_evt_formatter regardless.  This may be better to break into
separate calls for the really paranoid.

Otherwise, it derives the key name from the field_info of the token
and then assigns the str value as returned by tostring.

When its done with one round it uses the JSON Fastwriter to return
the std::string back...

The third party JSON-CPP library had one line changed: The fastwriter
part of it would output a newline for us. This was already being handled
and would produce two new lines.  So I removed that from the library.

JSON is a finished standard and I don't expect many "upgrades" to the
library so I think this is a change we can live with.