autoconf: rename configure.in to configure.ac

configure.ac has been the recommended name for autoconf input for several
years now. Newer autotools start to complain about the configure.in, so we
finally change it.

Makefile.am

@@ -20,7 +20,7 @@ config_includedir = $(ipseclibdir)/include
 nodist_config_include_HEADERS = config.h
 endif
 
-Android.common.mk :	Android.common.mk.in configure.in
+Android.common.mk :	Android.common.mk.in configure.ac
 		$(AM_V_GEN) \
 		sed \
 		-e "s:\@PACKAGE_VERSION\@:$(PACKAGE_VERSION):" \
@@ -70,4 +70,4 @@ clean-local: cov-reset-common
 		@find $(top_builddir)/{src,scripts} -name "*.gcno" -delete
 		@rm -rf apidoc
 
-.PHONY: cov-reset-common cov-reset cov-report coverage
+.PHONY: cov-reset-common cov-reset cov-report coverage