Added Xapian::DFR_PL2Weight to the registry.
Added DFR_PL2Weight to the makefile in Csharp bindings.
Added DFR_PL2Weight to the makefile for java bindings.
Test for conversion of invalid parameter to default value.
Added test for dfr_pl2weight.
Added feature tests for DFR_PL2Weight.
Removed trailing whitespaces from api_weight.cc.
Removed trailing whitespaces from dfr_pl2weight.cc
Removed trailing whitespaces from weight.h.
Added one more feature test for DFR_PL2Weight.
Test file for the DFR_PL2 weighting scheme.
Placed <cmath> after "xapian/weight.h".