Set memory limit for LZMA decompression

Otherwise malicious LZMA compressed files could consume large amounts
of memory when decompressed.

According to the xz man page, files compressed with `xz -9` currently
require 65 MB to decompress, so set the limit to 100 MB.

Should fix bug 786696.
diff --git a/xzlib.c b/xzlib.c
index 782957f..f43632b 100644
--- a/xzlib.c
+++ b/xzlib.c
@@ -408,7 +408,7 @@
         state->strm = init;
         state->strm.avail_in = 0;
         state->strm.next_in = NULL;
-        if (lzma_auto_decoder(&state->strm, UINT64_MAX, 0) != LZMA_OK) {
+        if (lzma_auto_decoder(&state->strm, 100000000, 0) != LZMA_OK) {
             xmlFree(state->out);
             xmlFree(state->in);
             state->size = 0;