Calls termux_git_clone_src if TERMUX_PKG_SRCURL ends with .git, and
termux_download_src_archive and termux_extract_src_archive otherwise.
termux_step_extract_package has been split up into the latter two
functions.
termux_step_post_extract_package has been renamed to
termux_step_post_get_source to reflect these changes.
Henrik Grimler