Corrected @{path/file/type/media} regressions.

:is_media_type() now behaves as expected with respect to input strings, thus
correcting previously broken behavior in :make_grub2_boot_image().

"The chimes entwine
 Varietals in orbit
 Twixt contorted echoes,
 Unseasonable stentorian woes,
 And gentiums tented in the bloom:
 The ostentatious livid choir.

 The thickest season blows."