[wp] Use PTEST_DIR for sessions

src/plugins/wp/tests/test_config_qualif

 PLUGIN: wp
-CMD: @frama-c@ -wp -wp-par 1 -wp-share @PTEST_SHARE_DIR@ -wp-msg-key shell -wp-warn-key pedantic-assigns=inactive -wp-report @PTEST_SUITE_DIR@/../qualif.report -wp-session @PTEST_SUITE_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session@PTEST_CONFIG@ -wp-cache-env -wp-cache replay @PTEST_FILE@
+CMD: @frama-c@ -wp -wp-par 1 -wp-share @PTEST_SHARE_DIR@ -wp-msg-key shell -wp-warn-key pedantic-assigns=inactive -wp-report @PTEST_SUITE_DIR@/../qualif.report -wp-session @PTEST_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session@PTEST_CONFIG@ -wp-cache-env -wp-cache replay @PTEST_FILE@
 OPT:

src/plugins/wp/tests/wp_eva/test_config_qualif

-CMD: @frama-c@ -no-autoload-plugins -load-module eva,scope,reduc,wp -eva -eva-no-print -eva-verbose 0 @PTEST_FILE@ -then -reduc -reduc-gen-annot all -then -no-reduc -then -wp -wp-par 1 -wp-share @PTEST_SHARE_DIR@ -wp-msg-key shell -wp-report tests/qualif.report -wp-session @PTEST_SUITE_DIR@/oracle@PTEST_CONFIG@/@PTEST_NAME@.@PTEST_NUMBER@.session -wp-cache-env -wp-cache replay @PTEST_FILE@
+CMD: @frama-c@ -no-autoload-plugins -load-module eva,scope,reduc,wp -eva -eva-no-print -eva-verbose 0 @PTEST_FILE@ -then -reduc -reduc-gen-annot all -then -no-reduc -then -wp -wp-par 1 -wp-share @PTEST_SHARE_DIR@ -wp-msg-key shell -wp-report tests/qualif.report -wp-session @PTEST_DIR@/oracle@PTEST_CONFIG@/@PTEST_NAME@.@PTEST_NUMBER@.session -wp-cache-env -wp-cache replay @PTEST_FILE@
 OPT:

src/plugins/wp/tests/wp_tip/clear.i

 /* run.config
 
-   OPT: -wp-par 1 -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_SUITE_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
+   OPT: -wp-par 1 -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
 */
 /* run.config_qualif
    DONTRUN:

src/plugins/wp/tests/wp_tip/induction_typing.i

 /* run.config
 
-   OPT: -wp-par 1 -wp-prop X -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_SUITE_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
+   OPT: -wp-par 1 -wp-prop X -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
 */
 /* run.config_qualif
    DONTRUN:

src/plugins/wp/tests/wp_tip/modmask.i

 /* run.config
 
-   OPT: -wp-par 1 -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_SUITE_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
+   OPT: -wp-par 1 -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
 
-   OPT: -wp-par 1 -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_SUITE_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
+   OPT: -wp-par 1 -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
 */
 /* run.config_qualif
    DONTRUN:

src/plugins/wp/tests/wp_tip/split.i

 /* run.config
 
-   OPT: -wp-par 1 -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_SUITE_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
+   OPT: -wp-par 1 -wp-no-print -wp-prover qed,tip -wp-msg-key script -wp-session @PTEST_DIR@/@PTEST_NAME@.@PTEST_NUMBER@.session
 */
 /* run.config_qualif
    DONTRUN:

src/plugins/wp/tests/wp_typed/user_init.i

 /* run.config_qualif
-   EXECNOW: rm -rf @PTEST_SUITE_DIR@/oracle@PTEST_CONFIG@/@PTEST_NAME@.1.session/script
+   EXECNOW: rm -rf @PTEST_DIR@/oracle@PTEST_CONFIG@/@PTEST_NAME@.1.session/script
    OPT: -wp-prop=-lack,-tactic
    OPT: -wp-prop=tactic -wp-auto=wp:split,wp:range -wp-prover=tip,alt-ergo
    OPT: -wp-prop=lack