Change ProcessMachCore to search for both a user-process dyld binary
and a mach kernel in all the pages of the core file.  If it finds
a user-process dyld binary, assume this is a user process that had
a copy of the mach kernel in memory when it crashed (e.g. lldb doing
kernel debugging) even though we found the kernel binary first.

Also, change the error messages about sections extending past the end
of the file to be warnings and make the messages sound less severe.
Most user process core files have one section that isn't included in
the file and there's no reason to worry people about that.

<rdar://problem/14473235> 


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@190741 91177308-0d34-0410-b5e6-96231b3b80d8