Change gcore in order to get rid of the procfs support and use FreeBSD's
specific interfaces. Main changes:
- now gcore recognizes threads within the the process and handle dumps on
a thread scope
- the process to be analyzed should be stopped while gcore runs
- gcore may not work with processes that are being debugged with gdb or
truss
- ptrace may let interruptible calls to return EINTR, thus dirtying
signals handling within the process
Sponsored by: Sandvine Incorporated
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