add 'head' field to PerlIOl struct

This allows any layer to find the top of the layer stack,
or more specifically, the entry in PL_perlio that points to
the top.

Needed for the next commit, which will implement a reference counting
scheme.

There's currently a bug in MakeMaker which causes several extensions to
miss the dependency on perliol.h having changed, so this commit includes
a gratuitous whitespace change to perl.h to hopefully force recompilation.

1 files changed, 1 insertions, 0 deletions

diff --git a/perl.h b/perl.h
index 4f66da2cc3..1be51b2253 100644
--- a/perl.h
+++ b/perl.h
@@ -8,6 +8,7 @@
  *
  */
 
+
 #ifndef H_PERL
 #define H_PERL 1