Add bash shell function to make python work like it should.

bootstrap/win/profile.d.python.sh

+#!/bin/bash
+# This alias allows invocations of `python` to work as expected under msys bash.
+# In particular, it detects if stdout+stdin are both attached to a pseudo-tty,
+# and if so, invokes python in interactive mode. If this is not the case, or
+# the user passes any arguments, python will be invoked unmodified.
+python() {
+  if [[ $# > 0 ]]; then
+    python.exe "$@"
+  else
+    readlink /proc/$$/fd/0 | grep pty > /dev/null
+    TTY0=$?
+    readlink /proc/$$/fd/1 | grep pty > /dev/null
+    TTY1=$?
+    if [ $TTY0 == 0 ] && [ $TTY1 == 0 ]; then
+      python.exe -i
+    else
+      python.exe
+    fi
+  fi
+}