add cabal flag for use with debian's older version of aws, which is now patched with the necessary stuff

debian/control

@@ -14,7 +14,7 @@ Build-Depends:
 	libghc-cryptohash-dev,
 	libghc-dataenc-dev,
 	libghc-utf8-string-dev,
-	libghc-aws-dev (>= 0.10.2),
+	libghc-aws-dev (>= 0.9.2),
 	libghc-conduit-dev,
 	libghc-resourcet-dev,
 	libghc-dav-dev (>= 1.0) [amd64 i386 kfreebsd-amd64 kfreebsd-i386 powerpc],

debian/rules

@@ -8,6 +8,10 @@ export RELEASE_BUILD=1
 %:
 	dh $@
 
+# Debian currently has a patched aws 0.9.2, rather than the newer 0.10.2.
+override_dh_auto_configure:
+	debian/cabal-wrapper configure -fPatchedAWS
+
 # Not intended for use by anyone except the author.
 announcedir:
 	@echo ${HOME}/src/git-annex/doc/news

git-annex.cabal

@@ -34,6 +34,10 @@ Description:
 Flag S3
   Description: Enable S3 support
 
+Flag PatchedAWS
+  Description: Building on system, like Debian, with old AWS patched to support git-annex
+  Default: False
+
 Flag WebDAV
   Description: Enable WebDAV support
 
@@ -151,7 +155,11 @@ Executable git-annex
     CPP-Options: -DWITH_CRYPTOHASH
 
   if flag(S3)
-    Build-Depends: aws (>= 0.10.2), conduit, resourcet
+    Build-Depends: conduit, resourcet
+    if flag(PatchedAWS)
+      Build-Depends: aws (>= 0.9.2)
+    else
+      Build-Depends: aws (>= 0.10.2)
     CPP-Options: -DWITH_S3
 
   if flag(WebDAV)