Fix man page substitutions

Fills in version & section info in cvt.1 and fixes meson warning:

man/meson.build:4: WARNING: The variable(s) 'appmansuffix', 'filemansuffix',
 'vendorversion' in the input file 'man/cvt.man' are not present in the given configuration data.

Signed-off-by: Alan Coopersmith alan.coopersmith@oracle.com

(Based on Xorg's meson.build)