syntax: move distro-specific files down to a subdirectory, syntax/extra/

doc/sample.nanorc.in

@@ -221,6 +221,8 @@
 # include "@PKGDATADIR@/python.nanorc"
 # include "@PKGDATADIR@/sh.nanorc"
 
+## In @PKGDATADIR@/extra/ you can find some syntaxes that are
+## specific for certain distros or for less common languages.
 
 ## If <Tab> should always produce four spaces when editing a Python file,
 ## independent of the settings of 'tabsize' and 'tabstospaces':

syntax/Makefile.am

@@ -5,12 +5,10 @@ pkgdata_DATA =	asm.nanorc \
 		cmake.nanorc \
 		c.nanorc \
 		css.nanorc \
-		debian.nanorc \
 		default.nanorc \
 		elisp.nanorc \
 		email.nanorc \
 		fortran.nanorc \
-		gentoo.nanorc \
 		go.nanorc \
 		groff.nanorc \
 		guile.nanorc \
@@ -37,10 +35,14 @@ pkgdata_DATA =	asm.nanorc \
 		ruby.nanorc \
 		rust.nanorc \
 		sh.nanorc \
-		spec.nanorc \
 		tcl.nanorc \
 		tex.nanorc \
 		texinfo.nanorc \
 		xml.nanorc
 
-EXTRA_DIST = $(pkgdata_DATA)
+nobase_pkgdata_DATA = \
+		extra/debian.nanorc \
+		extra/gentoo.nanorc \
+		extra/spec.nanorc
+
+EXTRA_DIST = $(pkgdata_DATA) $(nobase_pkgdata_DATA)