archivepath is interpreted differently depending on the value of archiveexploded

[jonsyu1]

Problem: archivepath is interpreted as directory when exploded and file when unexploded.

Suggestion: We may not want to break API, but this should be noted in both the wiki.

Suggestion: The rolling filewriter should also report the error when the rolling filewriter fails to create the unexploded archive (the user probably specified a directory, since that's the expected value when archiveexploded is true.

Repro steps:
Configure seelog with archivepath pointing to an existing directory and archiveexploded="false"
<rollingfile formatid="ourlogStdout" type="date" filename="./var/log/axiom.log" datepattern="2006-01-02_03:04:05" archivetype="gzip" maxrolls="1" archivepath="./var/log" archiveexploded="false"/>

Expected:
Error creating unexploded archive at "./var/log": is a directory

Actual:
Silent failure: no archive created, files continue to be deleted on roll

Conversely, the rolling filewriter should report an error when it points to a file.

Repro steps:
Configure seelog with archivepath pointing at an existing file and archiveexploded="true"
<rollingfile formatid="ourlogStdout" type="date" filename="./var/log/axiom.log" datepattern="2006-01-02_03:04:05" archivetype="gzip" maxrolls="1" archivepath="./var/log/axiom.log.tgz" archiveexploded="true"/>

Expected:
Error creating exploded archive under `"./var/log/axiom.log.tgz": is a file

Actual:
Silent failure: no archives created, files continue to be deleted on roll

Bottom line:
This is pretty easily recognizable, but I don't want users to change their archiveexploded setting and accidentally lose logs on roll.