minor avl-2.0.3 problems - mishandling of const

[Peter Breitenlohner]

Hi,

in order to compile cleanly with 'gcc -Wall -Wcast-qual' I have applied the
attached small patch to the copies of your avl.c in the TeX Live tree (used
for pdfTeX and luaTeX).  I am confident you can translate these changes back
to avl.w and strongly suspect there are similar minor glitches in the rest
of your code (not used for TeX Live).

Regards
Peter Breitenlohner <address@hidden>