tags: don't read .hgtags fnodes from tags cache files
Now that we have a standalone and shared cache for .hgtags fnodes, the
.hgtags fnodes stored in the tags cache files are redundant.
Upcoming patches will change the format of the tags cache files to
remove this data and to improve the validation. To prepare for this, we
change the tags reading code to ignore all but the tip .hgtags fnodes
entries in existing tags cache files.
All fnodes lookups now go through our new shared cache, which is why
test output changed. Format of tags cache files has not yet changed.
Mercurial supports several ways to specify individual revisions.
A plain integer is treated as a revision number. Negative integers are
treated as sequential offsets from the tip, with -1 denoting the tip,
-2 denoting the revision prior to the tip, and so forth.
A 40-digit hexadecimal string is treated as a unique revision
identifier.
A hexadecimal string less than 40 characters long is treated as a
unique revision identifier and is referred to as a short-form
identifier. A short-form identifier is only valid if it is the prefix
of exactly one full-length identifier.
Any other string is treated as a bookmark, tag, or branch name. A
bookmark is a movable pointer to a revision. A tag is a permanent name
associated with a revision. A branch name denotes the tipmost open branch head
of that branch - or if they are all closed, the tipmost closed head of the
branch. Bookmark, tag, and branch names must not contain the ":" character.
The reserved name "tip" always identifies the most recent revision.
The reserved name "null" indicates the null revision. This is the
revision of an empty repository, and the parent of revision 0.
The reserved name "." indicates the working directory parent. If no
working directory is checked out, it is equivalent to null. If an
uncommitted merge is in progress, "." is the revision of the first
parent.