Fix "parameter has incomplete type" on GCC 3.4.6
Fix this GCC 3.4.6 warning, which becomes an error
if configure --enable-debug adds -Werror to CFLAGS:
[CC] src/document/css/apply.o
In file included from /home/Kalle/src/elinks-0.12/src/document/html/internal.h:6,
from /home/Kalle/src/elinks-0.12/src/document/css/apply.c:35:
/home/Kalle/src/elinks-0.12/src/document/html/parser.h:149: warning: parameter has incomplete type
In file included from /home/Kalle/src/elinks-0.12/src/document/css/apply.c:35:
/home/Kalle/src/elinks-0.12/src/document/html/internal.h:125: warning: parameter has incomplete type
Even without this warning, "enum html_special_type;"
would not be standard C89.