term: use an argument vector for termopen().

Old behaviour: termopen('cmd') would run `&shell &shcf "cmd"`, which
caused the functional tests to fail on some systems due to the process
not "owning" the terminal. Also, it is inconsistent with jobstart().

Modify termopen() so that &shell is not invoked, but maintain the old
behaviour with :terminal. Factor the common code for building the
argument vector from jobstart() and modify the functional tests to call
termopen() instead of :terminal (fixes #2354).

Also:
 * Add a 'name' option for termopen() so that `:terminal {cmd}` produces
   a buffer named "term//{cwd}/{cmd}" and termopen() users can customize
   the name.
 * Update the documentation.
 * Add functional tests for `:terminal` sinse its behaviour now differs
   from termopen(). Add "test/functional/fixtures/shell-test.c" and move
   "test/functional/job/tty-test.c" there, too.

Helped-by: Justin M. Keyes <@justinmk>

1 files changed, 25 insertions, 0 deletions

diff --git a/test/functional/fixtures/shell-test.c b/test/functional/fixtures/shell-test.c
new file mode 100644
index 0000000000..5fa8a58049
--- /dev/null
+++ b/test/functional/fixtures/shell-test.c
@@ -0,0 +1,25 @@
+// A simple implementation of a shell for testing
+// `termopen([&sh, &shcf, '{cmd'}])` and `termopen([&sh])`.
+//
+// If launched with no arguments, prints "ready $ ", otherwise prints
+// "ready $ {cmd}\n".
+
+#include <stdio.h>
+#include <string.h>
+
+int main(int argc, char **argv)
+{
+  fprintf(stderr, "ready $ ");
+
+  if (argc == 3) {
+    // argv should be {"terminal-test", "EXE", "prog args..."}
+    if (strcmp(argv[1], "EXE") != 0) {
+      fprintf(stderr, "first argument must be 'EXE'\n");
+      return 2;
+    }
+
+    fprintf(stderr, "%s\n", argv[2]);
+  }
+
+  return 0;
+}