support for ext_ptt, compiles OKbut not tested

git-svn-id: https://svn.code.sf.net/p/freetel/code/codec2-dev@1871 01035d8c-6547-0410-b346-abe4f91aad63
support for odd numbers of carriers to support 450 bit/s and Nc=5

git-svn-id: https://svn.code.sf.net/p/freetel/code/codec2-dev@1872 01035d8c-6547-0410-b346-abe4f91aad63