Introduce nvim namespace: Move files.

Move files from src/ to src/nvim/.
- src/nvim/ becomes the new root dir for nvim executable sources.
- src/libnvim/ is planned to become root dir of the neovim library.

src/nvim/os/users.c

@@ -0,0 +1,87 @@
+// users.c -- operating system user information
+
+#include <uv.h>
+
+#include "os/os.h"
+#include "garray.h"
+#include "misc2.h"
+#ifdef HAVE_PWD_H
+# include <pwd.h>
+#endif
+
+// Initialize users garray and fill it with os usernames.
+// Return Ok for success, FAIL for failure.
+int os_get_usernames(garray_T *users)
+{
+  if (users == NULL) {
+    return FAIL;
+  }
+  ga_init(users, sizeof(char *), 20);
+
+# if defined(HAVE_GETPWENT) && defined(HAVE_PWD_H)
+  char *user;
+  struct passwd *pw;
+
+  setpwent();
+  while ((pw = getpwent()) != NULL) {
+    // pw->pw_name shouldn't be NULL but just in case...
+    if (pw->pw_name != NULL) {
+      ga_grow(users, 1);
+      user = (char *)vim_strsave((char_u*)pw->pw_name);
+      if (user == NULL) {
+        return FAIL;
+      }
+      ((char **)(users->ga_data))[users->ga_len++] = user;
+    }
+  }
+  endpwent();
+# endif
+
+  return OK;
+}
+
+// Insert user name in s[len].
+// Return OK if a name found.
+int os_get_user_name(char *s, size_t len)
+{
+  return os_get_uname(getuid(), s, len);
+}
+
+// Insert user name for "uid" in s[len].
+// Return OK if a name found.
+// If the name is not found, write the uid into s[len] and return FAIL.
+int os_get_uname(uid_t uid, char *s, size_t len)
+{
+#if defined(HAVE_PWD_H) && defined(HAVE_GETPWUID)
+  struct passwd *pw;
+
+  if ((pw = getpwuid(uid)) != NULL
+      && pw->pw_name != NULL && *(pw->pw_name) != NUL) {
+    vim_strncpy((char_u *)s, (char_u *)pw->pw_name, len - 1);
+    return OK;
+  }
+#endif
+  snprintf(s, len, "%d", (int)uid);
+  return FAIL;  // a number is not a name
+}
+
+// Returns the user directory for the given username.
+// The caller has to free() the returned string.
+// If the username is not found, NULL is returned.
+char *os_get_user_directory(const char *name)
+{
+#if defined(HAVE_GETPWNAM) && defined(HAVE_PWD_H)
+  struct passwd *pw;
+  if (name == NULL) {
+    return NULL;
+  }
+  pw = getpwnam(name);
+  if (pw != NULL) {
+    // save the string from the static passwd entry into malloced memory
+    char *user_directory = (char *)vim_strsave((char_u *)pw->pw_dir);
+    return user_directory;
+  }
+#endif
+  return NULL;
+}
+