Fixes for compiling on gcc-4.9.1 (ubuntu)

Adding "this->" avoids errors like:

...src/core/distributions/evolution/characterhistory/BiogeographicTreeHistoryCtmc.h:1083:32:
error: there are no arguments to ‘removeParameter’ that depend on a
template parameter, so a declaration of ‘removeParameter’ must be
available [-fpermissive]
     removeParameter( siteRates );