Fix the use of --checkpoint without explicit --checkpoint-action

* src/checkpoint.c (checkpoint_finish_compile): Set default action,
if necessary.
* tests/checkpoint/defaults.at: New testcase.
* tests/checkpoint/dot-compat.at: New testcase.
* tests/checkpoint/dot-int.at: New testcase.
* tests/checkpoint/dot.at: New testcase.
* tests/checkpoint/interval.at: New testcase.
* tests/Makefile.am: Add new testcases.
* tests/testsuite.at Include new testcases.

.gitignore

@@ -8,6 +8,7 @@
 .deps
 .emacs*
 .libs
+.gdbinit
 ABOUT-NLS
 ChangeLog
 INSTALL
@@ -28,3 +29,4 @@ libtool
 m4
 rmt
 stamp-h1
+TAGS