Fixed conversion warnings from clang

Plus some other details. (Option '-Wuninitialized' was removed from
the makefile because it is already enabled by -Wall.)

testes/libs/makefile

@@ -5,7 +5,7 @@ LUA_DIR = ../../
 CC = gcc
 
 # compilation should generate Dynamic-Link Libraries
-CFLAGS = -Wall -std=gnu99 -O2 -I$(LUA_DIR) -fPIC -shared
+CFLAGS = -Wall -std=c99 -O2 -I$(LUA_DIR) -fPIC -shared
 
 # libraries used by the tests
 all: lib1.so lib11.so lib2.so lib21.so lib2-v2.so