Move generated includes to their own directory to avoid conflicts.

Fixes #1051, mosh fails to build on case-insensitive filesystems.

XXX This isn't perfect because autoconf/automake drop several extra
files in the directory anyway.

src/include/Makefile.am

@@ -0,0 +1,14 @@
+BUILT_SOURCES = version.h
+nodist_INCLUDES = version.h
+
+clean-local:
+	@rm -rf version.h
+
+version.h:	../../VERSION
+	@test -s $<
+	@printf '#define BUILD_VERSION "%s"\n' "$$(cat $<)" > $@.new
+	@set -e; if ! diff -q $@ $@.new > /dev/null 2>&1; then \
+		mv -f $@.new $@; \
+	fi
+	@rm -f $@.new
+