test/hfp: test invalid commands

test/hfp: test parsing of apple extensions

test/hfp: test lower command

test/hfp: add long command

hfp: remove trailing newline/carriage return in custom command event

test/hfp: verify line buffer for custom commands

test/hfp: add tests for custom commands

test/hfp: fix warnings

test/hfp: test alpha field in call waiting

test/hfp: add +CLIP test data

test: only compile CppUTest files with c++ compiler