tests: add a substitution pattern for dates in HTTP headers and LFS payload This will be useful when printing HTTP headers and JSON payload received from an LFS server. The RFC 1123 date masking has uses elsewhere too.

xdiff: fix a hard crash on Windows The xdiff case of test-diff-antipatience.t started crashing in the C extension with 882657a9f768 (with 6a71a5ba666b backported so it compiles). There are a few more instances of 'long', but this resolves the crashing.