if file is inaccessible for _apt, disable privilege drop in acquire

We had a very similar method previously for our own private usage, but
with some generalisation we can move this check into the acquire system
proper so that all frontends profit from this compatibility change.

As we are disabling a security feature here a warning is issued and
frontends are advised to consider reworking their download logic if
possible.

Note that this is implemented as an all or nothing situation: We can't
just (not) drop privileges for a subset of the files in a fetcher, so in
case you have to download some files with and some without you need to
use two fetchers.

1 files changed, 2 insertions, 0 deletions

diff --git a/apt-pkg/acquire.h b/apt-pkg/acquire.h
index 10025a6ef..3e5ca41cd 100644
--- a/apt-pkg/acquire.h
+++ b/apt-pkg/acquire.h
@@ -303,9 +303,11 @@ class pkgAcquire
 
    /** \brief Get the head of the list of items. */
    inline ItemIterator ItemsBegin() {return Items.begin();};
+   inline ItemCIterator ItemsBegin() const {return Items.begin();};
 
    /** \brief Get the end iterator of the list of items. */
    inline ItemIterator ItemsEnd() {return Items.end();};
+   inline ItemCIterator ItemsEnd() const {return Items.end();};
    
    // Iterate over queued Item URIs
    class UriIterator;