Function to read one line of any size from a stream and return it in

Function to read one line of any size from a stream and return it in

	* camel-stream-buffer.c (camel_stream_buffer_read_line): Function
	to read one line of any size from a stream and return it in
	allocated memory.

Also add camel-stream-buffer.h to camel.h and CamelStreamBuffer to
camel-types.h.