Allow -q to be repeated for very quiet output

Even with the -q flag specified, tracing output is still mixed
with messages about signals and process exit status, which is
often irrelevant.  Allow the -q option to be repeated to force
the suppression of signals / exit status info too.

* defs.h: Change 'qflag' from 'bool' to 'unsigned int'.
* strace.1: Document ability to repeat '-q' option.
* strace.c: Allow '-q' to be repeated to quieten process
exit status and signal messages.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
diff --git a/defs.h b/defs.h
index 291b8fb..58cdf99 100644
--- a/defs.h
+++ b/defs.h
@@ -539,7 +539,7 @@
 extern cflag_t cflag;
 extern bool debug_flag;
 extern bool Tflag;
-extern bool qflag;
+extern unsigned int qflag;
 extern bool not_failing_only;
 extern bool show_fd_path;
 /* are we filtering traces based on paths? */