[gl2ps] index conflicts with <string.h> header file

[Daniel J Sebald]

Hello gl2ps Developers,

In gl2ps.c are a few instances of a variable called "index".  There is a 
global name "index" via <string.h> header that creates a 
shadow-global-name warning when compiled.  A simple fix is to change the 
name of the variable in a half dozen places.

gl2ps.c: In function 'gl2psListPointer':
gl2ps.c:573:54: warning: declaration of 'index' shadows a global declaration
gl2ps.c: In function 'gl2psFindRoot':
gl2ps.c:1409:38: warning: declaration of 'index' shadows a global 
declaration
gl2ps.c: In function 'gl2psBuildBspTree':
gl2ps.c:1525:12: warning: declaration of 'index' shadows a global 
declaration
gl2ps.c: In function 'gl2psPrintPostScriptBeginViewport':
gl2ps.c:3117:9: warning: declaration of 'index' shadows a global declaration
gl2ps.c: In function 'gl2psPrintPDFBeginViewport':
gl2ps.c:4761:9: warning: declaration of 'index' shadows a global declaration
gl2ps.c: In function 'gl2psPrintSVGBeginViewport':
gl2ps.c:5196:9: warning: declaration of 'index' shadows a global declaration
gl2ps.c: In function 'gl2psPrintPGFBeginViewport':
gl2ps.c:5426:9: warning: declaration of 'index' shadows a global declaration
gl2ps.c: In function 'gl2psBeginPage':
gl2ps.c:5613:9: warning: declaration of 'index' shadows a global declaration

Dan Sebald