Change tryopen to allow opening multiple files during one run.
Return number of errors at end.

Adapt test cases.

regress/open_nonarchive.test

diff --git a/regress/open_nonarchive.test b/regress/open_nonarchive.test
index 979a26e..c2a9fd5 100644
--- a/regress/open_nonarchive.test
+++ b/regress/open_nonarchive.test
@@ -4,3 +4,4 @@
 args Makefile.am
 return 1
 stdout opening `Makefile.am' returned error 19
+stderr 1 errors