u* tools: detect language/runtime automatically

[goldshtn]

By default, the u* tools (uobjnew, uflow, etc.) can detect the language/runtime present in the target process by inspecting its command line or its loaded libraries (/proc/PID/maps). The -l switch can then be used for overriding the default.

It might also make sense to make all the tools use -l for consistency, instead of having the language as a positional parameter.

Suggested by @brendangregg