+ * Many commands use --dashed-option as a operation mode selector
+ (e.g. "git tag --delete") that the user can use at most one
+ (e.g. "git tag --delete --verify" is a nonsense) and you cannot
+ negate (e.g. "git tag --no-delete" is a nonsense). parse-options
+ API learned a new OPT_CMDMODE macro to make it easier to implement
+ such a set of options.
+
+ * OPT_BOOLEAN() in parse-options API was misdesigned to be "counting
+ up" but many subcommands expect it to behave as "on/off". Update
+ them to use OPT_BOOL() which is a proper boolean.
+
+ * "git gc" exits early without doing a double-work when it detects
+ that another instance of itself is already running.
+
+ * Under memory pressure and/or file descriptor pressure, we used to
+ close pack windows that are not used and also closed filehandle to
+ an open but unused packfiles. These are now controlled separately
+ to better cope with the load.