RFR(S) 8017498: JVM crashes when native code calls sigaction(sig) where sig>=0x20

[Calvin Cheung]

Please review a small fix:
http://cr.openjdk.java.net/~ccheung/8017498/webrev/

Bug:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8017498
https://jbs.oracle.com/bugs/browse/JDK-8017498

Summary:
I couldn't reproduce the crash as stated in the bug report.
However, I saw hang in the native code when sig value is much
greater than 32, e.g. 132. Fix suggested by David H. is to add
another check for the sig value is less than MAXSIGNUM in jsig.c.
With the fix, the hang is gone and the regression test is for
testing the hang condition.

Testing:
JPRT
jtreg test on test/runtime with the new regression test
Aurora adhoc vm.signal and vm.quick tests on linux
     (in progress, no failure so far)

thanks,
Calvin