Fix reporting of redefinition errors by adding a set of error/warning

Fix reporting of redefinition errors by adding a set of error/warning
reporting functions that take a parameter for the line to be displayed in
addition to the the line used for sorting.  This allows the "previously
defined" message to use the standard errwarn line resolution functions.

The resulting error messages look like gcc output.

Reported by: Edouard Gomez <ed.gomez@free.fr>

svn path=/trunk/yasm/; revision=1074