[prodcommit] Speed optimisation
Previously, `prodcommit` used `git submodule summary --cached` as the basis of the commit log it generated, and then proceeded to throw away much of the information it provided. Now, this command is extremely slow, especially on Windows machines where it can take a minute or more to execute. Replace this with one of the plumbing commands that `git submodule` used internally, viz `git diff-index --cached HEAD`, which provides most of the information it needed, but far faster (more like 0.1 seconds). The one catch is that it reports the state of all changed items in the tree, not just the submodules, but due to the way we structure superprojects, we can simply assume that anything within the top-level `RiscOS` directory is a submodule. The commands that determine whether a given submodule is a regression, as well as the embedded invocation of `git commit`, remain relatively slow operations on Windows, but the overall process is typically now about 3 times faster than it was previously.
Showing with 7 additions and 9 deletions