* Add perl* utools man page links

Matches other languages, related to commit 9162be45.

* uthreads: explicitly list C as supported

uthreads supports C (pthreads) thread tracing, make this explicit.

Earlier use of -l java and -l none unchanged.

Add the corresponding man page and usage examples.

* Add Tcl support for ucalls / uflow / uobjnew / ustat

For some reason we need to use proc__args instead of proc__entry
in uflow.py to get similar results as with e.g. Python.

* cc: bcc function to detect the language of a process

bcc_procutils_language looks into /proc/$pid/cmdline, /proc/$pid/exe,
and /proc/$pid/maps to determine the language.
Python wrapper takes a list of candidate languages; if the detected
language is not part of the list, None is returned.

* u* tools: automatically detect the language

Uses the detect_language bcc helper. -l switch can override the
detected language. In uthreads and ucalls, the language can be
overwritten to 'none' to trace pthreads and syscalls respectively.

All tools use the -l switch to set the language, for consistency.