Fix some linking issues.

On Ubuntu 16.04 I had trouble making this compile. There was one notable
change required - the libraries to link (ppm.so and LIBS) need to be
given after the file being compiled. It also seems helpful to link
ppm.so against the required libraries, otherwise how will slapd know to
find libcrack?

Finally, I added -Wl,-rpath=. to ppm_test meaning it can be run directly
without needing to set the library path.

Makefile

@@ -40,13 +40,13 @@ TESTS=./unit_tests.sh
 all: 	ppm ppm_test
 
 ppm_test: 
-	$(CC) $(LDAP_INC) $(LDAP_LIBS) $(LIBS) ppm.so -o ppm_test ppm_test.c 
+	$(CC) $(LDAP_INC) $(LDAP_LIBS) -Wl,-rpath=. -o ppm_test ppm_test.c ppm.so $(LIBS)
 
 ppm.o:
 	$(CC) $(OPT) -c $(INCS) ppm.c
 
 ppm: clean ppm.o
-	$(CC) $(LDAP_INC) -shared -o ppm.so ppm.o
+	$(CC) $(LDAP_INC) -shared -o ppm.so ppm.o $(CRACK_LIB)
 
 install: ppm
 	cp -f ppm.so $(LIBDIR)