Error compiling git when docbooc2k is custom compiled.

Hello.

I've compiled docbook2x to --prefix=/opt/docbook2X. When building git make fails not finding docbook2x-texi, but /opt/docbook2X/bin is in the PATH. Investigating I've found that default build of docbook2X from sources creates file with the following names:

docbook2man docbook2texi

So I use option --program-transform-name="s/^docbook2/docbook2x-/" when compiling docbook2X.

Please allow in building git detect the name of docbook2X when using default options when compiling docbook2X.