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.

gdb/python/lib/gdb/__init__.py

@@ -85,15 +85,14 @@ def execute_unwinders(pending_frame):
     Returns:
         gdb.UnwindInfo instance or None.
     """
-    for objfile in _gdb.objfiles():
+    for objfile in objfiles():
         for unwinder in objfile.frame_unwinders:
             if unwinder.enabled:
                 unwind_info = unwinder(pending_frame)
                 if unwind_info is not None:
                     return unwind_info
 
-    current_progspace = _gdb.current_progspace()
-    for unwinder in current_progspace.frame_unwinders:
+    for unwinder in current_progspace().frame_unwinders:
         if unwinder.enabled:
             unwind_info = unwinder(pending_frame)
             if unwind_info is not None:
@@ -163,3 +162,25 @@ def GdbSetPythonDirectory(dir):
     # attributes
     reload(__import__(__name__))
     auto_load_packages()
+
+def current_progspace():
+    "Return the current Progspace."
+    return selected_inferior().progspace
+
+def objfiles():
+    "Return a sequence of the current program space's objfiles."
+    return current_progspace().objfiles()
+
+def solib_name (addr):
+    """solib_name (Long) -> String.\n\
+Return the name of the shared library holding a given address, or None."""
+    return current_progspace().solib_name(addr)
+
+def block_for_pc(pc):
+    "Return the block containing the given pc value, or None."
+    return current_progspace().block_for_pc(pc)
+
+def find_pc_line(pc):
+    """find_pc_line (pc) -> Symtab_and_line.
+Return the gdb.Symtab_and_line object corresponding to the pc value."""
+    return current_progspace().find_pc_line(pc)