Currently, the Cobertura plugin configuration has a "Cobertura xml report pattern". In this box,
you enter an expression that identifies which files you wish to be considered for Cobertura
reporting. However, there is currently no way to configure which directory this pattern is relative
to. It does not allow you to enter system-wide absolute paths, nor does it allow relative paths
that go outside of the base directory using "..". This can be problematic for users whose build
scripts (Ant build.xml, etc.) generate the Cobertura XML files within the workspace, but not
within the module root, or in a location outside the workspace entirely. In many cases, the plugin not
recognizing these files was misreported as a bug (see Issue 1423).

To support these use cases, I suggest the following:
-Add a new "advanced" configuration text field, "Cobertura xml report base directory"
-If the value is not specified/blank, treat it as if it contains ${DEFAULT} (see below)
-If the value contains the expression ${DEFAULT}, replace that with the absolute
path of the same directory as is currently used by default (module root unless
multi-module Subversion, in which case workspace root)
-If the value contains the expression ${MODULE_ROOT}, replace that with the absolute
path of the module root
-If the value contains the expression ${WORKSPACE}, replace that with the absolute
path of the workspace root
-When publishing cobertura results, evaluate the "Cobertura xml report pattern" relative to the
"Cobertura xml report base directory".

By putting the field in the Advanced section, this should prevent the new option from overly
inconveniencing users who don't need it. By keeping the behavior the same when the new field is
blank, we should preserve backwards-compatibility with existing configurations. By allowing arbitrary
absolute paths, or paths relative to either the module root or workspace, we should hopefully meet the
needs of all users.