v0.7.3

• A spawn tells a file's kind from its first 256 bytes, not the whole file:
  a Node script's #! line and a binary image's first bytes are read
  through the tree's own descriptors where it offers them, so spawning a
  multi-megabyte binary by path no longer reads all of it.
• process.dlopen of a missing file fails as Node's does, with
  ERR_DLOPEN_FAILED and the dynamic linker's message, not require's
  MODULE_NOT_FOUND; loaders such as Prisma's report on that code.
• A child's fd stdio holds its own reference to the parent's description
  (TreeDescriptors.dup), as fork and dup2 give it on Linux: a parent that
  hands a log file to a long-lived child and closes its fd (twin-world's
  pgliteUp) no longer cuts the child's output.