Building Subversion 1.6 requires GNU grep 2.5

Subversion 1.6 requires GNU grep 2.5 or later. See the provided mailing list URL for more information. 
Subversion did not used to require GNU grep 2.5 and does not currently document this requirement. I 
believe it would be preferable to once again allow Subversion to be built with earlier GNU grep, or with 
non-GNU grep. If this is not possible or desired, then the GNU grep 2.5 requirement should be 
documented in the INSTALL file.

http://subversion.tigris.org/ds/viewMessage.do?dsForumId=1065&dsMessageId=2374300

Original issue reported by ryandesign