Don't overflow if computing approximate percentage

Don't overflow if computing approximate percentage

* nnbabyl.el (nnbabyl-retrieve-headers):
* nndiary.el (nndiary-retrieve-headers):
* nneething.el (nneething-retrieve-headers):
* nnmbox.el (nnmbox-retrieve-headers):
* nnmh.el (nnmh-retrieve-headers):
* nnml.el (nnml-retrieve-headers):
* nnspool.el (nnspool-retrieve-headers):
* nntp.el (nntp-retrieve-headers, nntp-retrieve-articles):
Prefer (floor (* 100.0 NUMERATOR) DENOMINATOR) when calculating
progress-report percentages and the like.  This avoids problems
if (* 100 NUMERATOR) would overflow.

* gnus-registry.el (gnus-registry-import-eld):
* registry.el (registry-reindex):
Use (* 100.0 ...) rather than (* 100 ...) to avoid int overflow issues.