whereis: do not ignore trailing numbers

whereis: do not ignore trailing numbers

The commands diff and diff3 are so distinct that their manual pages
should not be mixed in whereis output.

Theoretically this works for commands and binaries with links to each
other, e.g. gpg and gpg2, but if gpg is version 1 and gpg2 is version 2
then manual pages do not match either.

Also the while loop does not decrement "i" while incrementing "dp". The
effect of this is that the output of whereis depends on manual pages
being compressed or not.

The easiest solution is to not ignore trailing numbers.

Signed-off-by: Samanta Navarro <ferivoz@riseup.net>