seafile-client: depend on python2, install pymodule 'future', fix shebang

Issue https://github.com/termux/termux-packages/issues/4699.

packages/seafile-client/app-seaf-cli.patch

@@ -0,0 +1,9 @@
+diff -uNr seafile-7.0.4/app/seaf-cli seafile-7.0.4.mod/app/seaf-cli
+--- seafile-7.0.4/app/seaf-cli	2019-12-06 10:34:31.000000000 +0200
++++ seafile-7.0.4.mod/app/seaf-cli	2019-12-26 12:25:08.093119398 +0200
+@@ -1,4 +1,4 @@
+-#!/usr/bin/env python
++#!/usr/bin/env python2
+ #-*- coding:utf-8 -*-
+ # pylint: disable=E1121
+ 

packages/seafile-client/build.sh

@@ -2,9 +2,10 @@ TERMUX_PKG_HOMEPAGE=http://seafile.com
 TERMUX_PKG_DESCRIPTION="Seafile is a file syncing and sharing software with file encryption and group sharing"
 TERMUX_PKG_LICENSE="Apache-2.0"
 TERMUX_PKG_VERSION=7.0.4
+TERMUX_PKG_REVISION=1
 TERMUX_PKG_SRCURL=https://github.com/haiwen/seafile/archive/v${TERMUX_PKG_VERSION}.tar.gz
 TERMUX_PKG_SHA256=d33d6de57b9dc8083aecde78abbd00684f7cda6a36ec8fd00749c7c8236a2a8e
-TERMUX_PKG_DEPENDS="ccnet, libcurl"
+TERMUX_PKG_DEPENDS="ccnet, libcurl, python2"
 TERMUX_PKG_BREAKS="seafile-client-dev"
 TERMUX_PKG_REPLACES="seafile-client-dev"
 TERMUX_PKG_BUILD_IN_SRC=true
@@ -19,3 +20,10 @@ termux_step_post_configure() {
 	cd $TERMUX_PKG_SRCDIR/lib
 	python $TERMUX_PREFIX/bin/searpc-codegen.py $TERMUX_PKG_SRCDIR/lib/rpc_table.py
 }
+
+termux_step_create_debscripts() {
+	cat <<- EOF > ./postinst
+	#!$TERMUX_PREFIX/bin/sh
+	pip2 install future
+	EOF
+}