sanitizeFilePath was changed to sanitize leading '.', but ImportFeed was
running it on parts of the template. So eg the leading '.' in the extension
got sanitized.
Note the added case for sanitizeLeadingFilePathCharacter ('/':_)
-- this was added because, if the template is title/episode and the title
is not set, it would expand to "/episode". So this is another potential
security fix.
* addurl --preserve-filename: New option, uses server-provided filename
without any sanitization, but with some security checking.
Not yet implemented for remotes other than the web.
* addurl, importfeed: Avoid adding filenames with leading '.', instead
it will be replaced with '_'.
This might be considered a security fix, but a CVE seems unwattanted.
It was possible for addurl to create a dotfile, which could change
behavior of some program. It was also possible for a web server to say
the file name was ".git" or "foo/.git". That would not overrwrite the
.git directory, but would cause addurl to fail; of course git won't
add "foo/.git".
sanitizeFilePath is too opinionated to remain in Utility, so moved it.
The changes to mkSafeFilePath are because it used sanitizeFilePath.
In particular:
isDrive will never succeed, because "c:" gets munged to "c_"
".." gets sanitized now
".git" gets sanitized now
It will never be null, because sanitizeFilePath keeps the length
the same, and splitDirectories never returns a null path.
Also, on the off chance a web server suggests a filename of "",
ignore that, rather than trying to save to such a filename, which would
fail in some way.
