Downgrade rust-bindgen to 0.25.5

There is an issue when building on Linux when using 0.26.0 or higher, so
keep to a version that still works on Mac and Linux.

cargo test passes

CHANGELOG.md

@@ -3,6 +3,10 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [0.6.6] - 2017-07-08
+### Changed
+- Downgrade to version 0.25.5 of `bindgen` library to avoid errors on Linux.
+
 ## [0.6.5] - 2017-07-07
 ### Changed
 - Add `compare_images()` method to `MagickWand` type.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "magick_rust"
-version = "0.6.5"
+version = "0.6.6"
 authors = ["Nathan Fiedler <nathanfiedler@fastmail.fm>"]
 description = "Selection of Rust bindings for the ImageMagick library."
 homepage = "https://github.com/nlfiedler/magick-rust"
@@ -14,5 +14,6 @@ build = "build.rs"
 libc = ">=0.2"
 
 [build-dependencies]
-bindgen = "0.26.2"
+# bindgen 0.26.x results in "already been defined in this module" errors (bug #687)
+bindgen = "0.25.5"
 pkg-config = "0.3.9"

build.rs

@@ -50,6 +50,7 @@ fn main() {
 
         // Geneate the bindings.
         let mut builder = bindgen::Builder::default()
+            .no_unstable_rust()
             .emit_builtins()
             .ctypes_prefix("libc")
             .raw_line("extern crate libc;")