Maria 5.3 bzr compile warnings in GCC 4.6

[Andrew Hutchings]

GCC 4.6 (Fedora 15) triggers a warning on variables that are written to and not read (it previously triggered in Drizzle for error variables that were set and not used). Currently failing with compile-pentium64-debug-max:

ma_dyncol.c: In function 'dynamic_column_update_many':
ma_dyncol.c:1750:11: error: variable 'copy' set but not used [-Werror=unused-but-set-variable]

Workaround of course is not to build in maintainer mode.