When looking up an object by name, allow prefix matches if no direct match
is found. This allows one to, for example, match libc entry probes with:
# dtrace -n 'pid$target:libc.so::entry' -c ./foo
instead of requiring "libc.so.7" or a glob.
Also remove proc_obj2map() as it currently just duplicates the
functionality of proc_name2map(). It's supposed to take a Solaris
link-map ID as a paramter, but support for this isn't implemented and
isn't required to support DTrace's pid provider.
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