[Dvipng] small fix to configure.ac

[Moraes, Mark]

On Solaris and lots of other Unix variants, 'which' is a csh script that
takes a long time to run, and at least on my Solaris, produces output
that fails to work with cp (I'm still a bit puzzled why).  Anyway, using
the sh builtin 'type' is much faster and works well.  (Solaris 8 sh
doesn't support 'type -p', alas)

        Mark.

*** configure.ac-       Mon Feb 27 07:05:56 2006
--- configure.ac        Thu May 25 19:56:04 2006
***************
*** 187,193 ****
    TEXMF_CNF=`kpsewhich texmf.cnf`
    AC_MSG_RESULT([$TEXMF_CNF])
    AC_MSG_CHECKING([for psfonts.map])
!   cp `which kpsewhich` .
    PSFONTS_MAP=`./kpsewhich psfonts.map`
    rm -f ./kpsewhich
    if test -n "$PSFONTS_MAP"; then
--- 187,193 ----
    TEXMF_CNF=`kpsewhich texmf.cnf`
    AC_MSG_RESULT([$TEXMF_CNF])
    AC_MSG_CHECKING([for psfonts.map])
!   cp `type kpsewhich | awk '$2 == "is" {print $3}'` .
    PSFONTS_MAP=`./kpsewhich psfonts.map`
    rm -f ./kpsewhich
    if test -n "$PSFONTS_MAP"; then