move the C sources to the subfolder pgf again for backwards compatibility

src/runtime/c/Makefile.am

@@ -3,21 +3,21 @@ lib_LTLIBRARIES = libpgf.la
 pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = libpgf.pc
 
-pgfincludedir=$(includedir)
+pgfincludedir=$(includedir)/pgf
 pgfinclude_HEADERS = \
-	pgf.h
+	pgf/pgf.h
 
 libpgf_la_SOURCES = \
-	db.cxx \
-	db.h \
-	text.cxx \
-	text.h \
-	pgf.cxx \
-	reader.cxx \
-	reader.h \
-	data.h \
-	expr.h \
-	namespace.h
+	pgf/db.cxx \
+	pgf/db.h \
+	pgf/text.cxx \
+	pgf/text.h \
+	pgf/pgf.cxx \
+	pgf/reader.cxx \
+	pgf/reader.h \
+	pgf/data.h \
+	pgf/expr.h \
+	pgf/namespace.h
 
 libpgf_la_LDFLAGS = "-no-undefined"