Added check for libz.

Author: rakshasa

configure.ac

@@ -55,10 +55,11 @@ TORRENT_WITHOUT_STATFS
 
 CC_ATTRIBUTE_VISIBILITY
 
-AX_PTHREAD([], AC_MSG_ERROR([requires pthread]))
+AX_PTHREAD
+AX_CHECK_ZLIB
 
-CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
-CXXFLAGS="$CXXFLAGS $PTHREAD_CFLAGS"
+CFLAGS="$PTHREAD_CFLAGS $CFLAGS"
+CXXFLAGS="$PTHREAD_CFLAGS $CXXFLAGS"
 LIBS="$PTHREAD_LIBS $LIBS"
 
 AC_ARG_ENABLE(openssl,