Revert "Drop support for building without network-uri."

This reverts commit fc3925a1cd.

Need it in stable w/o backports for the ancient autobuilder.

CHANGELOG

@@ -13,7 +13,6 @@ git-annex (6.20170301.2) UNRELEASED; urgency=medium
     in the warning message.
   * Windows: Improve handling of shebang in external special remote
     program, searching for the program in the PATH.
-  * Drop support for building without network-uri.
   * Drop support for building with old versions of dns and http-conduit.
 
  -- Joey Hess <id@joeyh.name>  Thu, 02 Mar 2017 12:51:40 -0400

git-annex.cabal

@@ -291,6 +291,10 @@ Flag Benchmark
   Description: Enable benchmarking
   Default: False
 
+Flag network-uri
+  Description: Get Network.URI from the network-uri package
+  Default: True
+
 Flag Dbus
   Description: Enable dbus support
 
@@ -314,8 +318,6 @@ Executable git-annex
    stm (>= 2.3),
    mtl (>= 2),
    uuid (>= 1.2.6),
-   network (>= 2.6),
-   network-uri (>= 2.6),
    process,
    data-default,
    case-insensitive,
@@ -374,6 +376,11 @@ Executable git-annex
   if os(Linux)
     GHC-Options: -optl-Wl,--as-needed
 
+  if flag(network-uri)
+    Build-Depends: network-uri (>= 2.6), network (>= 2.6)
+  else
+    Build-Depends: network (< 2.6), network (>= 2.4)
+
   if (os(windows))
     Build-Depends: Win32, Win32-extras, unix-compat (>= 0.4.1.3), setenv,
       process (>= 1.3.0.0)

stack.yaml

@@ -4,6 +4,7 @@ flags:
     production: true
     assistant: true
     pairing: true
+    network-uri: true
     s3: true
     testsuite: true
     webdav: true