Add more warning flags, fix a few new warnings

src/iomux_select.c

@@ -112,7 +112,7 @@ static int iomux_select_unregister_fd(struct IOMux *mux_, struct IOMuxFD *fd)
     size_t i;
     for(i = 0; i < mux->num_descriptors; i++) {
         if(fd == mux->descriptors[i]) {
-            int what = fd->what; //make sure we don't alter 'what' as seen from the user
+            unsigned int what = fd->what; //make sure we don't alter 'what' as seen from the user
             fd->what &= ~MUX_EV_MASK;
             iomux_select_update_events(mux_, fd);
             mux->descriptors[i] = NULL; //set the slot to NULL, the event loop needs to rebuild it.

src/ucore_murmurhash.c

@@ -20,7 +20,7 @@ uc_murmurmash2(const void *key, int len, uint32_t seed )
 
     while(len >= 4)
     {
-        uint32_t k = *(uint32_t *)data;
+        uint32_t k = *(const uint32_t *)data;
 
         k *= m; 
         k ^= k >> r; 

src/ucore_sprintbc.c

@@ -6,12 +6,12 @@ char*
 uc_sprintbc(char *result, unsigned char value)
 {
 	char *s = result;
-	unsigned char mask = ~((unsigned char) (~0) >> 1);
+	unsigned char mask = ~((unsigned char) (~0U) >> 1U);
 
 	if (s) {
 		while (mask) {
 			*s++ = (mask & value) ? '1' : '0';
-			mask >>= 1;
+			mask >>= 1U;
 		}
 		*s = '\0';
 	}