Handle improperly build image files gracefully

Handle improperly build image files gracefully

Images build improperly (by simply concatenating separate images) were accepted,
but anything after the first end-of-file record *silently* ignored. Now emit warning
for intel and motorola images upon non-whitespace after first end-of-file record but
continue reading anyway.
ST ships some images broken that way in their CubeMX packages ...

Change-Id: I0c5d08fa90070fed11fb805c5f0dc39817048176
Signed-off-by: Andreas Bolsch <hyphen0break@gmail.com>
Reviewed-on: http://openocd.zylin.com/4281
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>