Do not install empty /usr/bin/ directory

Regression was added in commit cae277e4377acc90ef787d09ed0d82968bbe809a
diff --git a/Makefile.in b/Makefile.in
index 1a40de2..02f090c 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -252,13 +252,13 @@
 install:
 	$(INSTALL) -d $(DESTDIR)$(includedir)/srtp
 	$(INSTALL) -d $(DESTDIR)$(libdir)
-	$(INSTALL) -d $(DESTDIR)$(bindir)
 	cp $(srcdir)/include/*.h $(DESTDIR)$(includedir)/srtp  
 	cp $(srcdir)/crypto/include/*.h $(DESTDIR)$(includedir)/srtp
 	if [ "$(srcdir)" != "." ]; then cp crypto/include/*.h $(DESTDIR)$(includedir)/srtp; fi
 	if [ -f libsrtp.a ]; then cp libsrtp.a $(DESTDIR)$(libdir)/; fi
 	if [ -f libsrtp.dll.a ]; then cp libsrtp.dll.a $(DESTDIR)$(libdir)/; fi
 	if [ -f libsrtp.$(SHAREDLIBSUFFIX) ]; then \
+		$(INSTALL) -d $(DESTDIR)$(SHAREDLIB_DIR); \
 		cp libsrtp.$(SHAREDLIBSUFFIX) $(DESTDIR)$(SHAREDLIB_DIR)/; \
 		ln -sfn libsrtp.$(SHAREDLIBSUFFIX) $(DESTDIR)$(SHAREDLIB_DIR)/libsrtp.$(SHAREDLIBSUFFIXNOVER); \
 	fi