Make SVN backend more robust

The SVN backend failed when trying to access historical information on deleted files.

There's also an initial test case for the SVN backend, testing this issue
and issue 364, which is about a similar problem for renamed files.
Reverting any of these fixes breaks the test.

test/data/IDF_Scm_SvnTest/testrepository/conf/authz

@@ -0,0 +1,32 @@
+### This file is an example authorization file for svnserve.
+### Its format is identical to that of mod_authz_svn authorization
+### files.
+### As shown below each section defines authorizations for the path and
+### (optional) repository specified by the section name.
+### The authorizations follow. An authorization line can refer to:
+###  - a single user,
+###  - a group of users defined in a special [groups] section,
+###  - an alias defined in a special [aliases] section,
+###  - all authenticated users, using the '$authenticated' token,
+###  - only anonymous users, using the '$anonymous' token,
+###  - anyone, using the '*' wildcard.
+###
+### A match can be inverted by prefixing the rule with '~'. Rules can
+### grant read ('r') access, read-write ('rw') access, or no access
+### ('').
+
+[aliases]
+# joe = /C=XZ/ST=Dessert/L=Snake City/O=Snake Oil, Ltd./OU=Research Institute/CN=Joe Average
+
+[groups]
+# harry_and_sally = harry,sally
+# harry_sally_and_joe = harry,sally,&joe
+
+# [/foo/bar]
+# harry = rw
+# &joe = r
+# * =
+
+# [repository:/baz/fuz]
+# @harry_and_sally = rw
+# * = r