Make deliberate overriding (*) works with overwrites detection.
(*) first introduced by d0e9c52410
The following are decided to be deliberate override:
- articles using the `save_as` metadata
- pages using the `save_as` metadata
- template pages (always)
Pelican now exits in the following 2 cases:
- at least 2 not deliberate writes to the same file name (behaviour introduced
by the overwrite detection feature ff7410ce2a)
- at least 2 deliberate writes to the same file name (new behaviour)
Also added info logging when deliberate overrides are performed.
Switched to StandardError instead of IOError, thanks to @ametaireau and
@russkel.
a495527e2b