phabricator: avoid calling differential.getcommitmessage Previously, we call differential.getcommitmessage API to get commit messages. Now we read that from "Differential Revision" object fetched via "differential.query" API. This removes one API call per patch.

phabricator: rework phabread to reduce memory usage and round-trips This patch reworked phabread a bit so it fetches the lightweight "Differential Revision" metadata for a stack first. Then read other data. This allows the code to: a) send 1 request to get all `hg:meta` data instead of N requests b) patches are read in desired order, no need to buffer the output "b)" reduces the memory usage from O(N^2) to O(N) since we no longer keep old patch contents in memory. The above `N` means the number of patches in the stack.