Both Tickets and SHAMapV2 have been around for a while and don't
look like they will be enabled on the network soon. So they are
removed from the supportedAmendments list. This prevents Env
from automatically testing with Tickets or SHAMapV2 enabled,
although testing with those features can still be explicitly
specified.
Drive-by cleanups:
o supportedAmendments() returns a const reference rather than
a fresh vector on each call.
o supportedAmendments() implementation moved from Amendments.cpp
to Feature.cpp. Amendments.cpp deleted.
o supportedAmendments() declared in Feature.h. All other
declarations deleted.
o preEnabledAmendments() removed, since it was empty and only
used in one place. It will be easy to re-add when it is needed.
o jtx::all_features_except() renamed to
jtx::supported_features_except(), which is more descriptive.
o jtx::all_amendments() renamed to jxt::supported_amendments()
o jtx::with_features() renamed to with_only_features()
o Env_test.cpp adjusted since featureTickets is no longer
automatically enabled for unit tests.
This commit introduces the "SortedDirectories" amendment, which
addresses two distinct issues:
First, it corrects a technical flaw that could, in some edge cases,
prevent an empty intermediate page from being deleted.
Second, it sorts directory entries within a page (other than order
book page entries, which remain strictly FIFO). This makes insert
operations deterministic, instead of pseudo-random and reliant on
temporal ordering.
Lastly, it removes the ability to perform a "soft delete" where
the page number of the item to delete need not be known if the
item is in the first 20 pages, and enforces a maximum limit to
the number of pages that a directory can span.
