Subversion has support for expanding SVN keywords (like $Id) into

values, and whether a file or a diff contains an expanded form is up to

the value of the svn:keywords property at the time when the file/diff

was fetched or generated, and any discrepency could cause problems when

applying patches. To avoid this problem, our Subversion support fetches

the keywords and collapses them when fetching files or when normalizing

patches.
This only worked for standalone repositories, though, and didn't work in

the case of Beanstalk. In fact, it outright broke. Patch normalization

would attempt to access the Subversion repository using the user's API

key, which wasn't supported, and this would cause an error. We also

weren't able to guarantee getting collapsed versions of files out of the

repository (depending on the file content and svn:keywords at the time

when the file was committed).
Fortunately, to help address this, the Beanstalk team recently gave us

an API to fetch a file's properties on Subversion without needing any

direct access to the repository. This change makes use of this during

both file fetching and patch normalization.
To actually do the work of collapsing, the keyword collapsing code that

used to live within the SVNTool client class has been made available

in a more public utility function, along with all the aliases and other

state needed for it to operate. A new function was also introduced that

checks a file's content to see if it has expanded keywords, helping us

avoid unnecessary lookups.
Hosting services have also gained the ability to normalize patches.

Previously, this was only available in SCMTool, but now a new

Repository.normalize_patch() will call out to either

HostingService.normalize_patch() or SCMTool.normalize_patch(). By

default, this all ends up calling SCMTool.normalize_patch(), but

Beanstalk's able to override this to apply its keyword fetching and

collapsing for Subversion.

All unit tests pass.
Linked a Beanstalk repository with an API token. Manually tested

uploading a diff to it using a file that returned expanded keywords,

and using a diff that also had (hand-edited) expanded keywords. The

upload was successful, and the diff viewer showed collapsed versions

of all keywords.