relnotes: add 6.7.3

relnotes/6.7

@@ -1,3 +1,20 b''
+= Mercurial 6.7.3 =
+
+ * setup: display return code information about failed `hg` call
+ * bundle-spec: properly identify changegroup-less bundle
+ * bundle-spec: properly parse boolean configuration as boolean
+ * matchers: fix the bug in rust PatternMatcher that made it cut off early
+ * match: fix the "visitdir" method on "rootfilesin" matchers
+ * match: fix the rust-side bug in visit_children_set for rootfilesin matchers
+ * match: strengthen visit_children_set invariant, Recursive means "all files"
+ * wireprotoserver: ensure that output stream gets flushed on exception
+ * re2: make errors quiet
+ * dirstate-v2: add check of parent/child nodes being related when writing
+ * dirstate-v2: check that root nodes are at the root before writing
+ * rust-cpython: don't swallow the dirstate error message
+ * rust: blanket implementation of Graph for Graph references
+ * Various fixes to `admin::verify`
+
 = Mercurial 6.7.2 =
 
 Exceptional release following a large performance regression when cloning.