Bump down extra_float_digits to 2
Bump down extra_float_digits to 2

This is to avoid breaking 8.4 in preparation for fully supporting it
in an upcoming patch (see #199).

Note that the tests here do not correctly check for a required
extra_float_digits=3, since they still pass; this should be
reviewed further.

cbandy/go-pq,johto/pq,amaniak/pq,lib/pq,flynn/pq,calebthompson/pq,VividCortex/pq,ScriptRock/pq,everalbum/pq,ympons/pq,StabbyCutyou/pq,ympons/pq,erichnascimento/pq,jnewmano/pq,sammi/pq,jnewmano/pq,bugreplaydev/pq,bugreplaydev/pq,dongzerun/pq,stvp/pq,springning/pq,beni55/pq,henrylee2cn/pq