git: Add attributes file to enforce line endings

Ensure that we don't accidentally end up with Windows line endings in
the repository or change binary files' line endings.

Signed-off-by: Ken Raffenetti <raffenet@mcs.anl.gov>

.gitattributes

@@ -0,0 +1,18 @@
+# Set the default behavior, in case people don't have core.autocrlf set.
+* text=auto
+
+# Explicitly declare text files you want to always be normalized and converted
+# to native line endings on checkout.
+*.c text
+*.h text
+
+# Declare files that will always have CRLF line endings on checkout.
+*.sln text eol=crlf
+
+# Denote all files that are truly binary and should not be modified.
+*.png     binary
+*.jpg     binary
+*.pdf     binary
+*.ps      binary
+*.tar.bz2 binary
+*.tar.gz  binary