Add more methods to gdb.Progspace

Add more methods to gdb.Progspace

There are a number of global functions in the gdb Python module which
really should be methods on Progspace.  This patch adds new methods to
Progspace and then redefines these globals in terms of these new
methods.

This version has been rebased on the related changes that Simon
recently put in.

Built and regtested on x86-64 Fedora 28.

gdb/ChangeLog
2018-09-16  Tom Tromey  <tom@tromey.com>

	* python/lib/gdb/__init__.py (current_progspace, objfiles)
	(solib_name, block_for_pc, find_pc_line): New functions.
	(execute_unwinders): Update.
	* python/py-block.c (gdbpy_block_for_pc): Remove.
	* python/py-inferior.c (infpy_get_progspace): New function.
	(inferior_object_getset) <progspace>: Add.
	* python/py-progspace.c (pspy_objfiles): Rewrite.
	(pspy_solib_name, pspy_block_for_pc)
	(pspy_find_pc_line, pspy_is_valid): New functions.
	(progspace_object_methods): Add entries for solib_name,
	block_for_pc, find_pc_line, is_valid.
	* python/python-internal.h (gdbpy_block_for_pc)
	(build_objfiles_list): Don't declare.
	* python/python.c: Don't include solib.h.
	(gdbpy_solib_name, gdbpy_find_pc_line)
	(gdbpy_get_current_progspace, build_objfiles_list)
	(gdbpy_objfiles): Remove.
	(GdbMethods) <current_progspace, objfiles, block_for_pc,
	solib_name, find_pc_line>: Remove entries.

gdb/doc/ChangeLog
2018-09-16  Tom Tromey  <tom@tromey.com>

	* python.texi (Basic Python): Update docs for find_pc_line,
	solib_name.
	(Progspaces In Python): Update docs for current_progspace.
	Document block_for_pc, find_pc_line, is_valid, nsolib_name.
	Move method documentation before example.