NHDT substitution version 2.

Re-run nhgitset.pl to install.
"perldoc DEVEL/hooksdir/nhsub" for details.  General docs still to come.
Quick notes:
- "git nhsub" lets you apply substitutions to a file without involving any
  version control.
- When doing nhadd/nhcommit, the working directory WILL reflect the results
  of the substitutions.
Let's see what this breaks.

sys/amiga/.gitattributes

@@ -1 +1 @@
-*.p filter=NHtext merge=NHsubst
+*.p NHSUBST

sys/mac/.gitattributes

@@ -1 +1 @@
-NHDeflts filter=NHtext merge=NHsubst
+NHDeflts NHSUBST

sys/msdos/.gitattributes

@@ -1,4 +1,4 @@
-*.BC filter=NHtext merge=NHsubst
-*.bat filter=NHtext merge=NHsubst
-Makefile.* filter=NHtext merge=NHsubst
-Install.* filter=NHtext merge=NHsubst
+*.BC NHSUBST
+*.bat NHSUBST
+Makefile.* NHSUBST
+Install.* NHSUBST

sys/os2/.gitattributes

@@ -1 +1 @@
-Makefile.* filter=NHtext merge=NHsubst
+Makefile.* NHSUBST

sys/share/.gitattributes

@@ -1 +1 @@
-Makefile.* filter=NHtext merge=NHsubst
+Makefile.* NHSUBST

sys/unix/.gitattributes

@@ -1 +1 @@
-Makefile.* filter=NHtext merge=NHsubst
+Makefile.* NHSUBST

sys/unix/hints/.gitattributes

@@ -1 +1 @@
-* filter=NHtext merge=NHsubst
+* NHSUBST

sys/vms/.gitattributes

@@ -1 +1 @@
-Makefile.* filter=NHtext merge=NHsubst
+Makefile.* NHSUBST

sys/wince/.gitattributes

@@ -1,3 +1,3 @@
-*.ce filter=NHtext merge=NHsubst
-*.mak filter=NHtext merge=NHsubst
-*.bat filter=NHtext merge=NHsubst
+*.ce NHSUBST
+*.mak NHSUBST
+*.bat NHSUBST

sys/winnt/.gitattributes

@@ -1,4 +1,4 @@
-Install.nt filter=NHtext merge=NHsubst
-Makefile.* filter=NHtext merge=NHsubst
-*.rc filter=NHtext merge=NHsubst
-*.bat filter=NHtext merge=NHsubst
+Install.nt NHSUBST
+Makefile.* NHSUBST
+*.rc NHSUBST
+*.bat NHSUBST