The websockets support relies on bits support in Erlang. The src/Makefile used to contain a gmake shell command for checking the erts version to see if bits support was present. This change moves that test into the configure scripts and adds a new make variable to include.mk that src/Makefile can use instead. This keeps configuration checks out of the makefiles and in the configure script where they belong. Also fixed the test for bits support, which would have been incorrect once the erts major version number increases above 5 because it also unconditionally wanted the erts minor number to be greater than 6, so a major/minor version such as 6.0 would have failed.