Show line numbers in output for "info var/func/type"

Show line numbers in output for "info var/func/type"

The GDB commands "info variables", "info functions", and "info types" show
the appropriate list of definitions matching the given pattern.  They also
group them by source files.  But no line numbers within these source files
are shown.

The line number information is particularly useful to the user when a
simple "grep" doesn't readily point to a definition.  This is often the
case when the definition involves a macro, occurs within a namespace, or
when the identifier appears very frequently in the source file.

This patch enriches the printout of these commands by the line numbers and
adjusts affected test cases to the changed output where necessary.  The
new output looks like this:

  (gdb) i variables
  All defined variables:

  File foo.c:
  3:	const char * const foo;
  1:	int x;

The line number is followed by a colon and a tab character, which is then
followed by the symbol definition.  If no line number is available, the
tab is printed out anyhow, so definitions line up.

gdb/ChangeLog:

	* symtab.c (print_symbol_info): Precede the symbol definition by
	the line number when available.
	* NEWS: Advertise this enhancement.

gdb/doc/ChangeLog:

	* gdb.texinfo (Symbols): Mention the fact that "info
	variables/functions/types" show source files and line numbers.

gdb/testsuite/ChangeLog:

	* gdb.ada/info_types.exp: Adjust expected output to the line
	numbers now printed by "info var/func/type".
	* gdb.base/completion.exp: Likewise.
	* gdb.base/included.exp: Likewise.
	* gdb.cp/cp-relocate.exp: Likewise.
	* gdb.cp/cplusfuncs.exp: Likewise.
	* gdb.cp/namespace.exp: Likewise.
	* gdb.dwarf2/dw2-case-insensitive.exp: Likewise.