python/py3cairo: Fix building with the newer python.

Signed-off-by: Matteo Bernardini <ponce@slackbuilds.org>

python/py3cairo/py3cairo.SlackBuild

@@ -25,7 +25,7 @@
 PRGNAM=py3cairo
 SRCNAM=pycairo
 VERSION=${VERSION:-1.10.0}
-BUILD=${BUILD:-2}
+BUILD=${BUILD:-3}
 TAG=${TAG:-_SBo}
 
 if [ -z "$ARCH" ]; then
@@ -57,6 +57,8 @@ else
   LIBDIRSUFFIX=""
 fi
 
+export PYTHON=python3
+
 set -e
 
 rm -rf $PKG
@@ -73,7 +75,7 @@ find -L . \
  -o -perm 440 -o -perm 400 \) -exec chmod 644 {} \;
 
 patch -p1 < $CWD/pycairo-1.10.0-waf_unpack-1.patch
-wafdir=$(python3 ./waf unpack)
+wafdir=$(./waf unpack)
 pushd $wafdir
 patch -p1 < $CWD/pycairo-1.10.0-waf_python_3_4-1.patch
 popd
@@ -82,7 +84,7 @@ unset wafdir
 PYTHON="/usr/bin/python3" \
 CFLAGS="$SLKCFLAGS" \
 CXXFLAGS="$SLKCFLAGS" \
-python3 ./waf configure \
+./waf configure \
   --prefix=/usr \
   --libdir=/usr/lib${LIBDIRSUFFIX} \
   --sysconfdir=/etc \
@@ -90,8 +92,8 @@ python3 ./waf configure \
   --mandir=/usr/man \
   --docdir=/usr/doc/$PRGNAM-$VERSION
 
-python3 ./waf build
-DESTDIR=$PKG python3 ./waf install
+./waf build
+DESTDIR=$PKG ./waf install
 
 find $PKG -print0 | xargs -0 file | grep -e "executable" -e "shared object" | grep ELF \
   | cut -f 1 -d : | xargs strip --strip-unneeded 2> /dev/null || true