We use the information from various configure time checks to populate
paths.sh. The paths used are all absolute except for the python binary.
In the switch to a more comprehensive check for python by commit
fa05153e ("Make checking for python more predictable.") we ended up
using AC_CHECK_PROGS which checks for the program on the path and sets
the variable to the name of the program. This makes python inconsistent
with the other programs and seems to cause problems for MSYS2. Use
AC_PATH_PROGS instead which does the same check but sets the variable to
the absolute name of the program
Fixes#2047
Signed-off-by: Chris Packham <judge.packham@gmail.com>
