Generate an xz tar archive of the distribution

* configure.ac (AM_INIT_AUTOMAKE): Replace dist-bzip2 with dist-xz.
* Makefile.am: Update srpm target.
* make-dist: Update for dist-xz.
* strace.spec: Update Source tag.
* debian/watch: Update regexp.
* .gitignore: Add strace-*.tar.xz.
diff --git a/make-dist b/make-dist
index a4e598c..fb5d8ce 100755
--- a/make-dist
+++ b/make-dist
@@ -22,4 +22,4 @@
 
 make -s $j distcheck
 
-mv -f *.tar.bz2 ..
+mv -f strace-*.tar.xz ..