Don't insist on leveldb (or berkeley-db) since they are optional.

configure.ac

@@ -34,12 +34,6 @@ LIBS="$MARGO_LIBS $LIBS"
 CPPFLAGS="$MARGO_CFLAGS $CPPFLAGS"
 CFLAGS="$MARGO_CFLAGS $CFLAGS"
 
-PKG_CHECK_MODULES([LEVELDB],[leveldb],[],
-      AC_MSG_ERROR([Could not find working leveldb installation!]) )
-LIBS="$LEVELDB_LIBS $LIBS"
-CPPFLAGS="$LEVELDB_CFLAGS $CPPFLAGS"
-CFLAGS="$LEVELDB_CFLAGS $CFLAGS"
-
 # Checks for typedefs, structures, and compiler characteristics.
 AC_C_INLINE
 AC_TYPE_INT64_T