Add "core.eol" config variable

Introduce a new configuration variable, "core.eol", that allows the user
to set which line endings to use for end-of-line-normalized files in the
working directory.  It defaults to "native", which means CRLF on Windows
and LF everywhere else.

Note that "core.autocrlf" overrides core.eol.  This means that

[core]
	autocrlf = true

puts CRLFs in the working directory even if core.eol is set to "lf".

Signed-off-by: Eyvind Bernhardsen <eyvind.bernhardsen@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -556,6 +556,19 @@ enum auto_crlf {
 
 extern enum auto_crlf auto_crlf;
 
+enum eol {
+	EOL_UNSET,
+	EOL_CRLF,
+	EOL_LF,
+#ifdef NATIVE_CRLF
+	EOL_NATIVE = EOL_CRLF
+#else
+	EOL_NATIVE = EOL_LF
+#endif
+};
+
+extern enum eol eol;
+
 enum branch_track {
 	BRANCH_TRACK_UNSPECIFIED = -1,
 	BRANCH_TRACK_NEVER = 0,