environment: move comment_line_char from cache.h

This is one step towards making strbuf.c not depend upon cache.h.
Additional steps will follow in subsequent commits.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

environment.h

@@ -3,6 +3,13 @@
 
 #include "strvec.h"
 
+/*
+ * The character that begins a commented line in user-editable file
+ * that is subject to stripspace.
+ */
+extern char comment_line_char;
+extern int auto_comment_line_char;
+
 /*
  * Wrapper of getenv() that returns a strdup value. This value is kept
  * in argv to be freed later.