Preserve line endings during x-revision bumping

`snap` package currently has different line endings in `cabal unpack` and `cabal unpack --pristine`, which I find nasty as it makes automation harder.

I'm not sure where to report the problem, and I'm not aware of the design of this `x-revision` patching to suggest a fix. I understand it's a minor problem, but now line conversion is needed just to see a nice diff between two `.cabal` versions. It could be nice if hackage could prevent such breakage.

``` diff
$ diff -u src/snap-0.13.3.2/snap.cabal \
<(cat ../patched-snap/snap.cabal | tr -d '\r')
--- src/snap-0.13.3.2/snap.cabal 2014-11-25 06:32:06.000000000 +0200
+++ /dev/fd/63 2015-01-23 10:45:35.228471993 +0200
@@ -1,5 +1,6 @@
name: snap
version: 0.13.3.2
+x-revision: 1
synopsis: Top-level package for the Snap Web Framework
description:
This is the top-level package for the official Snap Framework libraries.
@@ -186,7 +187,7 @@
else
build-depends:
base >= 4.4 && < 5,
- lens >= 3.7.6 && < 4.7
+ lens >= 3.7.6 && < 4.8

extensions:
BangPatterns,
```

Without the conversion `diff` shows all lines differ.