depend on libosmocore 0.1.0

this creates a hard dependency to a certain base version of the library
diff --git a/openbsc/configure.in b/openbsc/configure.in
index 9e3c486..b733f78 100644
--- a/openbsc/configure.in
+++ b/openbsc/configure.in
@@ -18,7 +18,7 @@
 AC_SEARCH_LIBS(crypt, crypt,
     [LIBCRYPT="-lcrypt"; AC_DEFINE([VTY_CRYPT_PW], [], [Use crypt functionality of vty.])])
 
-PKG_CHECK_MODULES(LIBOSMOCORE, libosmocore)
+PKG_CHECK_MODULES(LIBOSMOCORE, libosmocore >= 0.1.0)
 
 dnl checks for header files
 AC_HEADER_STDC