convert: rename the "eol" global variable to "core_eol"

Yes, it is clear that "eol" wants to mean some sort of end-of-line thing,
but as the name of a global variable, it is way too short to describe what
kind of end-of-line thing it wants to represent. Besides, there are many
codepaths that want to use their own local "char *eol" variable to point
at the end of the current line they are processing.

This global variable holds what we read from core.eol configuration
variable. Name it as such.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

convert.c

@@ -113,10 +113,10 @@ static enum eol determine_output_conversion(enum action action)
 			return EOL_CRLF;
 		else if (auto_crlf == AUTO_CRLF_INPUT)
 			return EOL_LF;
-		else if (eol == EOL_UNSET)
+		else if (core_eol == EOL_UNSET)
 			return EOL_NATIVE;
 	}
-	return eol;
+	return core_eol;
 }
 
 static void check_safe_crlf(const char *path, enum action action,