Issue #2974 - Part 66: client.mk and configure.in shouldn't invoke Python 2.

This was unneeded on my system because I made sure the build system couldn't
find Python 2 on the PATH, forcing it to use Python 3. Many developers may
be in environments with both available, so this should be changed.

client.mk

@@ -66,7 +66,7 @@ endif
 
 SH := /bin/sh
 PERL ?= perl
-PYTHON ?= $(shell which python2.7 > /dev/null 2>&1 && echo python2.7 || echo python)
+PYTHON ?= $(shell which python3 > /dev/null 2>&1 && echo python3 || echo python)
 
 CONFIG_GUESS_SCRIPT := $(wildcard $(TOPSRCDIR)/build/autoconf/config.guess)
 ifdef CONFIG_GUESS_SCRIPT

configure.in

@@ -22,4 +22,4 @@ SRCDIR=$(dirname $0)
 TOPSRCDIR="$SRCDIR"
 export OLD_CONFIGURE="$SRCDIR"/old-configure
 
-which python2.7 > /dev/null && exec python2.7 "$TOPSRCDIR/configure.py" "$@" || exec python "$TOPSRCDIR/configure.py" "$@"
+which python3 > /dev/null && exec python3 "$TOPSRCDIR/configure.py" "$@" || exec python "$TOPSRCDIR/configure.py" "$@"