RFR: 8147500: The HashtableTextDump::get_num() should check for integer overflow

[Jiangli Zhou]

Please review the following improvements to HashtableTextDump::get_num() and HashtableTextDump::corrupted_if() described in JDK-8147500 <https://bugs.openjdk.java.net/browse/JDK-8147500>.

 - The HashtableTextDump::get_num() is use to parse an integer value from the input file. It should check for integer overflow and report error without continuing.
 - The HashtableTextDump::corrupted_if() should take an additional argument so caller can pass a meaningful error message.

Webrev: http://cr.openjdk.java.net/~jiangli/8147500/webrev.00/

Thanks,
Jiangli