Use FOO_CMD instead of FOO to avoid a conflict with a variable used
in the docproj port. TEX, LATEX, PDFTEX, JADETEX, and PDFJADETEX
has been renamed to TEX_CMD, LATEX_CMD, PDFTEX_CMD, JADETEX_CMD, and
PDFJADETEX_CMD for consistency. And TEXCMDS has been renamed
TEX_CMDSEQ because TEXCMDS and TEX_CMD are misleading names.

Discussed on: -doc