pidgin/pidgin

aim: Switch to new libpurple/finch distid/devids provided by AOL

The pidgin ids were already handled by a previous commit.

https://pidgin.im/pipermail/support/2017-January/029820.html
installed_m4=purple.m4
EXTRA_DIST=$(installed_m4)
m4datadir=$(datadir)/aclocal
m4data_DATA=$(installed_m4)