[Ada catchpoints] Fix "warning: failed to get exception name: No definition of \"e.full_name\" in current context"

Looking at testsuite results, I noticed this warning in an MI test:

 ~"\nCatchpoint "
 ~"2, "
 &"warning: failed to get exception name: No definition of \"e.full_name\" in current context.\n"
 ~"exception at 0x000000000040192d in foo () at /home/pedro/brno/pedro/gdb/mygit/src/gdb/testsuite/gdb.ada/mi_catch_ex/foo.adb:20\n"
 ~"20\t      raise Constraint_Error;  -- SPOT1\n"
 *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",exception-name="CONSTRAINT_ERROR",frame={addr="0x000000000040192d",func="foo",args=[],file="/home/pedro/brno/pedro/gdb/mygit/src/gdb/testsuite/gdb.ada/mi_catch_ex/foo.adb",fullname="/home/pedro/brno/pedro/gdb/mygit/src/gdb/testsuite/gdb.ada/mi_catch_ex/foo.adb",line="20"},thread-id="1",stopped-threads="all",core="5"
 (gdb)
 PASS: gdb.ada/mi_catch_ex.exp: continue until CE caught by all-exceptions catchpoint

The problem is that:

  - MI prints the breakpoint hit twice: once on the MI stream;
    another time on the console stream.

  - After printing the Ada catchpoint hit, gdb selects a non-current
    frame, from within the catchpoint's print_it routine.

So the second time the breakpoint is printed, the selected frame is no
longer the current frame, and then evaluating e.full_name in
ada_exception_name_addr fails.

This commit fixes the problem and enhances the gdb.ada/mi_catch_ex.exp
test to make sure the catchpoint hit is printed correctly on the
console stream too.

gdb/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	* ada-lang.c (ada_exception_name_addr_1): Add comment.
	(print_it_exception): Select the current frame.

gdb/testsuite/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	* gdb.ada/mi_catch_ex.exp (continue_to_exception): New procedure.
	(top level): Use it instead of mi_execute_to.

1 files changed, 9 insertions, 0 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 412aa97..3c5ab26 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -12183,6 +12183,8 @@ ada_unhandled_exception_name_addr_from_raise (void)
    (of any type), return the address in inferior memory where the name
    of the exception is stored, if applicable.
 
+   Assumes the selected frame is the current frame.
+
    Return zero if the address could not be computed, or if not relevant.  */
 
 static CORE_ADDR
@@ -12484,6 +12486,13 @@ print_it_exception (enum ada_exception_catchpoint_kind ex, bpstat bs)
   ui_out_field_int (uiout, "bkptno", b->number);
   ui_out_text (uiout, ", ");
 
+  /* ada_exception_name_addr relies on the selected frame being the
+     current frame.  Need to do this here because this function may be
+     called more than once when printing a stop, and below, we'll
+     select the first frame past the Ada run-time (see
+     ada_find_printable_frame).  */
+  select_frame (get_current_frame ());
+
   switch (ex)
     {
       case ada_catch_exception: