[BUGFIX] Warn about apc.enable_cli=0 on command line

When running a CLI script via typo3/cli_dispatch.phpsh,
using the APC caching backend will lead to errors like
> TYPO3 Exception #1232986877: Could not set value.

This patch checks if TYPO3 is running on CLI, and validates the
apc.enable_cli setting to give a proper error message.

Change-Id: Icbeb619fc2054634274b492df94dbbc89958a8b6
Resolves: #25274
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/28035
Reviewed-by: Ernesto Baschny
Reviewed-by: Andreas Fernandez
Tested-by: Andreas Fernandez
Reviewed-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn