gdb: New maint info line-table command.

gdb: New maint info line-table command.

Add a new command 'maint info line-table' to display the contents of
GDB's internal line table structure.  Useful when trying to understand
problems (within gdb) relating to line tables.

gdb/ChangeLog:

	* symmisc.c (maintenance_info_line_tables): New function.
	(maintenance_print_one_line_table): New function.
	(_initialize_symmisc): Register 'maint info line-table' command.
	* NEWS: Mention new command.

gdb/doc/ChangeLog:

	* gdb.texinfo (Symbols): Document new 'maint info line-table'
	command.

gdb/testsuite/ChangeLog:

	* gdb.base/maint.exp: New tests for 'maint info line-table'.