added pcpstream usage to signature lib code as well

src/signature.h

@@ -31,6 +31,7 @@
 #include "pcp.h"
 #include "uthash.h"
 #include "z85.h"
+#include "pcpstream.h"
 
 int pcpsign(char *infile, char *outfile, char *passwd, int z85, int detach);
 int pcpverify(char *infile, char *sigfile, char *id, int detach);