Fix: Spelling mistake

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5669 43c1dc8c-776e-4df2-8ef1-6e829299be21
Fix: Update configure.ac/makefile.am to recognise asterisk-trunk (asterisk-13). Compilation against asterisk-13 currently broken, needs fixing/more work. references #226.

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5670 43c1dc8c-776e-4df2-8ef1-6e829299be21