Substitute ADFLAGS_NOADOUBLE with ADVOL_NOADOUBLE, which gets automatically stuffed...

Substitute ADFLAGS_NOADOUBLE with ADVOL_NOADOUBLE, which gets automatically stuffed into
struct adouble via ad_init. This eleminates the need to call vol_no_adouble(vol) every time
in ad_open in order to pass ADFLAGS_NOADOUBLE with adflags, instead inside ad_open the func checks
ad->ad_options.
Remove forced adouble file creation from ad_metadata, this broke the clean ad_* API semantics of
only creating files with O_CREATE. Instead do it explicitly in enumerate where the original force
adouble patch grew from.