bug in texi2dvi, on Windows/Msys2 it cannot find tex

[Tomas Kalibera]

Hello,

texi2dvi on Msys2 doesn't find tex, because it incorrectly detects ";" 
as path separator (it is ":").

The problem is in the following code. With Msys2, OSTYPE is "msys", but 
MSYSTEM is upper-case "MSYS" and uname needs it that way:

# In the case of Msys, uname returns a value derived from MSYSTEM, as
# MSYSTEM is user configurable, it is not so safe to use it to detect
# Msys. It is safer to use OSTYPE, this is why we set MSYSTEM to
# $OSTYPE before calling uname
if test -n "$COMSPEC$ComSpec" \
   && MSYSTEM=$OSTYPE uname | $EGREP -iv 'cygwin|msys' >/dev/null; then
  path_sep=";"
else
  path_sep=":"
fi

I've reported this with more detail for Msys2 
(https://github.com/msys2/MSYS2-packages/issues/2901) but perhaps it is 
worth fixing upstream as the code was meant to support MSYS.

As a workaround, R on Windows currently uses "COMSPEC= texi2dvi" but it 
would be nice if this could be fixed.

Thanks
Tomas