test: move system includes to notmuch-test.h

This removes some redudant includes, and will also make it easier to
introduce "#define _GNU_SOURCE", which must come before all system
includes.

test/T562-lib-database.sh

@@ -9,10 +9,8 @@ test_begin_subtest "building database"
 test_expect_success "NOTMUCH_NEW"
 
 cat <<EOF > c_head
-#include <stdio.h>
-#include <notmuch.h>
 #include <notmuch-test.h>
-#include <talloc.h>
+
 int main (int argc, char** argv)
 {
    notmuch_database_t *db;

test/T563-lib-directory.sh

@@ -9,10 +9,8 @@ test_begin_subtest "building database"
 test_expect_success "NOTMUCH_NEW"
 
 cat <<EOF > c_head
-#include <stdio.h>
-#include <notmuch.h>
 #include <notmuch-test.h>
-#include <talloc.h>
+
 int main (int argc, char** argv)
 {
    notmuch_database_t *db;

test/T564-lib-query.sh

@@ -9,10 +9,8 @@ test_begin_subtest "building database"
 test_expect_success "NOTMUCH_NEW"
 
 cat <<EOF > c_head
-#include <stdio.h>
-#include <notmuch.h>
 #include <notmuch-test.h>
-#include <talloc.h>
+
 int main (int argc, char** argv)
 {
    notmuch_database_t *db;

test/T566-lib-message.sh

@@ -19,9 +19,8 @@ cat <<'EOF' > c_tail
 EOF
 
 cat <<EOF > c_head0
-#include <stdio.h>
-#include <notmuch.h>
 #include <notmuch-test.h>
+
 int main (int argc, char** argv)
 {
    notmuch_database_t *db;

test/T568-lib-thread.sh

@@ -24,9 +24,8 @@ cat <<'EOF' > c_tail
 EOF
 
 cat <<EOF > c_head
-#include <stdio.h>
-#include <notmuch.h>
 #include <notmuch-test.h>
+
 int main (int argc, char** argv)
 {
    notmuch_database_t *db;

test/T590-libconfig.sh

@@ -23,8 +23,6 @@ EOF
 }
 
 cat <<EOF > c_head
-#include <string.h>
-#include <stdlib.h>
 #include <notmuch-test.h>
 
 int main (int argc, char** argv)
@@ -639,8 +637,6 @@ cp notmuch-config.bak notmuch-config
 test_expect_equal_file EXPECTED OUTPUT
 
 cat <<EOF > c_head2
-#include <string.h>
-#include <stdlib.h>
 #include <notmuch-test.h>
 
 int main (int argc, char** argv)

test/T595-reopen.sh

@@ -6,8 +6,6 @@ test_description="library reopen API"
 add_email_corpus
 
 cat <<EOF > c_head
-#include <string.h>
-#include <stdlib.h>
 #include <notmuch-test.h>
 
 int main (int argc, char** argv)

test/T610-message-property.sh

@@ -6,10 +6,6 @@ test_description="message property API"
 add_email_corpus
 
 cat <<EOF > c_head
-#include <stdio.h>
-#include <string.h>
-#include <stdlib.h>
-#include <talloc.h>
 #include <notmuch-test.h>
 
 void print_properties (notmuch_message_t *message, const char *prefix, notmuch_bool_t exact) {

test/T620-lock.sh

@@ -9,9 +9,6 @@ if [ $NOTMUCH_HAVE_XAPIAN_DB_RETRY_LOCK -ne 1 ]; then
     test_subtest_known_broken
 fi
 test_C ${MAIL_DIR} <<'EOF'
-#include <unistd.h>
-#include <stdlib.h>
-#include <sys/wait.h>
 #include <notmuch-test.h>
 
 void

test/T640-database-modified.sh

@@ -10,11 +10,8 @@ test_begin_subtest "catching DatabaseModifiedError in _notmuch_message_ensure_me
 first_id=$(notmuch search --output=messages '*'| head -1 | sed s/^id://)
 
 test_C ${MAIL_DIR} <<EOF
-#include <unistd.h>
-#include <stdlib.h>
 #include <notmuch-test.h>
-#include <talloc.h>
-#include <assert.h>
+
 int
 main (int argc, char **argv)
 {

test/notmuch-test.h

@@ -1,7 +1,13 @@
 #ifndef _NOTMUCH_TEST_H
 #define _NOTMUCH_TEST_H
+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <talloc.h>
+#include <unistd.h>
+
 #include <notmuch.h>
 
 inline static void