Generates pstex/pstex_t from fig to accommodate xelatex
xelatex is note based on pdflatex (lualatex is) thus the \ifpdf macro returns false. As xelatex uses \ifpdf to identify the latex engine and thus will try to insert ps files instead of pdf ones.
This patch adds make rules to also generate pstex and pstex_t files.
Some refs: