build system fix: make uninstall now does not break the source directory

Remove installed headers (now using a directory name with the intended
capitalisation) rather than the copy in the local source directory.

server/Makefile

@@ -146,7 +146,7 @@ install: $(TARGET)
 	cp -v $(TARGET) $(DESTDIR)$(PREFIX)/bin/
 
 uninstall:
-	rm -f $(DESTDIR)$(PREFIX)/include/pEP/$(wildcard *.hh)
+	rm -f $(addprefix $(DESTDIR)$(PREFIX)/include/pEp/,$(wildcard *.hh))
 
 clean:
 	rm -vf *.a *.o */*.o *.d *.d.* $(TARGET) $(TESTS) encode_decode