Add support for "ALTER TABLE ... DROP COLUMN ..." commands.

FossilOrigin-Name: c844a331e78949850fde8ed95058cb34f863566944bc9e92e3ae042768f130e1

diff --cc manifest
index a595639ccc920f0fb2387b6f65807082eed608db,ef19b71a400b2fcea81f3b68551572bf375dbae9..7d02d42122adf543bd938f16111720deb9396a25
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Avoid\sinvoking\sthe\supdate\sor\spre-update\shooks\sduring\sVACUUM\soperations.
- D 2021-02-18T15:59:37.490
 -C Fix\sa\scrash\sthat\scould\soccur\sin\sALTER\sTABLE\sDROP\sCOLUMN\sif\sthe\ssqlite_schema\stable\swas\scorrupt.
 -D 2021-02-19T14:13:40.890
++C Add\ssupport\sfor\s"ALTER\sTABLE\s...\sDROP\sCOLUMN\s..."\scommands.
++D 2021-02-19T14:32:58.535
  F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
  F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
  F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@@ -1900,7 -1903,7 +1903,8 @@@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a9
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+ R a9f6b9c36a39e6908ea00fd7298f0619
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  U dan
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 -Z 77e2ec90698c4f83ecd6e0d769d5b14d
++Z c1e3973235fcf41f620261cabeb4df13

diff --cc manifest.uuid
index 81f136ebf3f14cdfd74a0c9d3bf9ccc3e6bc7ca4,d35260df6382c1c5be5db9ffaad9c450d8098213..a03f87c63b55af0be382581ec43330dab0bce827
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 3c25cb4ab8885a50e2a485fe76f5ffd5dd8ebe1306aca8c0989e0b7fd7dd18d2
 -126ee1ec4f3565c0cccca98885fa3665a641ea3df251511de16eed2a1c396124
++c844a331e78949850fde8ed95058cb34f863566944bc9e92e3ae042768f130e1