This introduces an API to plug custom filters to an input stream.
The caller gets get_stream_filter("path") to obtain an appropriate
filter for the path, and then uses it when opening an input stream
via open_istream(). After that, the caller can read from the stream
with read_istream(), and close it with close_istream(), just like an
unfiltered stream.
This only adds a "null" filter that is a pass-thru filter, but later
changes can add LF-to-CRLF and other filters, and the callers of the
streaming API do not have to change.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Before adding the streaming filter API to the conversion layer,
move the existing declarations related to the conversion to its
own header file.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
