#9 Better prototyping of errmsg

[Daniel Macks]

Change [a712d2] resolved an undeclared function warning. However, it hardcoded the prototype for a function that is actually declared elsewhere. Saner (and the way it's done in all other source files that call this function) would be to #include the header that has it (utils.h), which entails also adding -I../src to CFLAGS in Makefile.