[RFAv2 0/5] Use language mode in 'info [functions|variables|types]|rbreak'

[Philippe Waroquiers <philippe dot waroquiers at skynet dot be>]

The commands 'info [functions|variables|types]|rbreak' work
on the global program, not only in the current frame.
So in in mixed languages program, these commands examine and print
entities defined in different languages.

Now, GDB uses the current language to print all the results of
these commands, which is somewhat surprising.

For example, when the current frame is in Ada,
info function gethostbyname gives:
  File ../nss/getXXbyYY.c:
  87:	function gethostbyname (a1: access char) return access hostent;

This patch series ensures that these commands respect the 'set language auto'
setup, to print the results in the language used to define the printed
entities.

This is the second version of the patch series, which handles all the
comments of Eli and Pedro.

For the documentation, the changes are
  * gdb.texinfo: Added references to 'set language'.
  * NEWS: Better sentence, as suggested by Eli.

For the code and test, all suggestions of Pedro were done,
a.o. change the class name to scoped_switch_to_sym_language_if_auto
which is more clear, change the test to have a better gdb.sum.

Thanks for the review, ok to push ?